E36 & E34 Alarm Identification & Faults Guide - GR40, 2T, 3T, 3G EWS
BMW E32, E34 & E36 Immobiliser and Alarm Identification & Faults Guide - GR40, 2T, 3T, 3G EWS (Sigma, Gemel, Serpi Star) EWS I, EWS II
My aim is to post all the confirmed knowledge about the immobiliser and alarm systems listed above. Many thanks to all those that have given me updates.
NOTE: There is a lot of info here so please take the time to read it carefully. If you have read the guide and still can't work out what to do then post a question in the auto electrical part of the forum mentioning that you have read the guide. Please don't add questions to the end of the guide or PM me as our private message won't help others.
If you don’t have a BMW “branded” alarm but need help then your best bet is to try a dedicated alarm forum.
Do I Have an Immobiliser? - All E34s and E36s after Sept 1993 came with a factory fitted immobiliser system. There were three types, Drive Away Protection, EWS I and EWS II. Check the sticker on the front suspension turret under the bonnet to find your manufacture date.
Drive Away Protection: 9/93 to 12/93 - The Injection/Ignition systems are disabled if the car is "Double Locked"
EWS is BMW's "Electronische Wegfahrsperre" or Electronic Immobiliser". There were two versions of EWS used on the E34 and E36...
EWS I: 1/94 to 1/95 - Improved on the Drive Away Protection by adding a starter immobilisation circuit.
EWS II: 1/95 to end of production - Improved on EWS I by adding the Key Chip and Transponder to the immobiliser circuit. New ignition keys can be bought from the dealer pre-cut and pre-programmed for £30 plus, depending on the type. You'll need to take the V5 in your name plus some ID. Expect to wait around a week.
You can also use the CODE button of the 18 button On-Board Computer (OBC) if fitted, as additional protection with any of these systems.
The EWS Technical guide can be downloaded here... http://www.bimmerforums.co.uk/forum/...1&d=1218372283
If you are experiencing starting problems and it seems like the immobiliser is activated there are a few things you can check, however if the car turns over it is not the immobiliser as the starter system is disabled when EWS I and II are activated...
1) Early E36s have a starter immobilisation relay and this can wear out
2) Also on early E36s there is an issue with poor scuttle drainage which leads to flooding of the DME (ECU) compartment, see here...
http://www.bimmerforums.co.uk/forum...creen-scuttle-drains?highlight=scuttle+drains
http://www.pelicanparts.com/bmw/tech...DME-Repair.htm
http://forums.bimmerforums.com/forum....php?p=5552421
3) All the immobiliser systems above work on a double lock/unlock signal from the driver or passenger door or a signal that mimics this from the alarm. It's always worth trying to lock & unlock the car from the passenger side (less wear on the lock) to see if it allows the car to start.
4) EWS II keys can get damaged and the chip is not be recognised by the EWS system. Try another key to see if this cures the issue. Even the grey valet key and small emergency key have chips in them.
5) Also check No.3 in the alarm faults below - bootlid wiring.
What Alarm System Do I Have? - If you don’t have a fob the easy way to identify your alarm is to find the siren or the alarm module. Generally, most BMW E36 & E34 alarms were were dealer retrofit (apart from "National Versions" see below) and were made by Sigma (part of the Gemel group). Because of this the module and siren location can vary from car to car.
In the E36 the alarm module is usually in one of three places
1) Behind glovebox in the top slot of the module carrier (most common location)
2) Under the carpet in the passenger footwell (this is a bad location as it can become damp) See here... http://www.bimmerforums.co.uk/forum...ob-to-3G-alarm?highlight=syncing+adding+alarm (4th post)
3) Under the steering wheel in the module carrier (This is more common when the system has been fitted to a pre 96 car)
In the E34 it can usually be found under the rear seat.
The siren is usually in one of three places
1) Nearside (passenger side) inner wing (most common location)
2) Offside (driver side) inner wing
3) Bulkhead near the fuse box (320/325/323/328 only)
I can't find the siren or the module! - You need to check if there is a red LED button by the gearstick and movement sensors at the top of the windscreen pillars (not on Convertible). If you don't have these either then its likely you never had an alarm fitted.
Radio Remote Control (Central Locking) - Some models had factory fit remote central locking on the key, BMW call this their Radio Remote Control (RRC) system. If you need a replacement key and your car has EWS II you'll need to get one from the dealer as above. You'll still need to re-sync the central locking to the remote yourself here... http://www.bimmerforums.co.uk/forum...mote-programming?highlight=remote+programming
"National Version" Alarm Systems - In various countries (except the USA) BMW included the option of an alarm system as a factory fit. This system is linked directly to the RRC system above, the obvious difference being the flush fit LED next to the gear selector. Another way to check is if you have a large chrome topped micro switch on the O/S/F inner wing, just near the washer bottle. This system arms and disarms through the RRC three button key and works in a similar way to the 3G systems, in that it sends a double lock pulse to set the immobiliser and monitors the door / boot / bonnet sensors for intrusion. I have not seen a version of this system with motion sensors but am happy to be corrected. The siren is located inside the O/S/F wing behind the inner wheel arch cover underneath the washer bottle. This system seems to be pretty reliable with the only reported issue being some over-sensitivity to voltage drop with cars that have an old battery.
GR40 (also known as Anti-Theft System 3) - This system was used on both the E34 and E36 from around 1990 to 1992 and uses a static code. The two button fob can be programmed by following the instructions here... http://www.abacuscaralarms.co.uk/ala...rpi-remote.htm The siren is almost identical to the 3G (Mk1). Fobs turn up regularly on eBay for around £10.
2T & 3T - These systems used on the E36 & E34 up to 1996 and have a static code. The 2T is an alarm only but the 3T is also an immobiliser. Both systems use the single button black or grey "Domino" type AC38 type fob that can only be programmed by a BMW Dealer/BMW Independent/Sigma Alarm Agent or you can buy your own programmer. Both siren types are clearly identifiable by a sticker. Fobs turn up regularly on eBay for around £10. A similar system that uses the same fob is fitted to some Subaru & Renault models and can be programmed via a plug-in keypad - This doesn't work with the BMW version as the Sigma programmer works by communicating with the module via the LED.
The 2T and 3T are not very user friendly so many replace them with 3G Mk2 or an aftermarket system. Provided the alarm is unset then it can be removed by simply cutting it out, see here... http://www.bimmerforums.co.uk/forum/threads/81929-E36-Retrofit-3G-mk2-Alarm?highlight=alarm+removal
User Guide (1995) is here...http://s447.photobucket.com/albums/q...0Guide 1995/
3G Mk1 (sometimes known as 3C) – This system was used on the E34 & E36 up to 1996 and uses a static code The black "missing corner" single button fob is only user programmable with some difficulty. You’ll need a working fob, then you need to solder and de-solder connections on the new fob circuit to match as follows (thanks to http://forum.bmw5.co.uk)....
You will need…
A working (or known to have worked) fob to copy
A replacement fob to re-programme
A decent thin tip soldering iron, solder & flux
A de-soldering tool or de-soldering braid
Open the fob and turn it over so you can see the circuit board. There is an array of 3 x 7 solder pads (see red box in the photo).
The upper and lower rows determine the 'code' for the key fob. The pads either have a blob of solder joining them, or no solder at all. You need to replicate this pattern in your replacement fob using the 4 step re-programming example sequence below.
1) The yellow dots show the code pattern for your working fob
2) The orange dots show the code pattern for your new fob pattern
3) De-solder the orange dots in the wrong position, removing all traces of solder
4) Re-solder the missing dots to match the working fob
Re-assemble the fob, replace the battery (right way round) and test. If you have made a good job of your de-soldering and soldering all should be well.
The other option is programming by a BMW Dealer/BMW Independent/Sigma Alarm Agent. Only one siren type was used (see below). Fobs turn up regularly on eBay for around £10.
The alarm module comes in two parts. The module (the large bit) and the remote receiver (the small bit).
Those familiar with the 3G Mk2 below will note that the module is identical except for the absence of the coding switch. It is possible to upgrade the 3G Mk1 to a 3G Mk2 by replacing the entire module or just the remote receiver part but you need to check the wiring is identical.
For both the above systems you may have read articles on the web that state you can program the alarm by opening the boot, closing the door, turning the ignition on 5 times, etc. These instructions are for the USA spec alarm made by Alpine and apart from giving your neighbours a laugh they won’t do anything in UK spec cars regardless of the system you have.
3G Mk2 – This Thatcham Cat 1 system came in when the E36 was facelifted in 1996 and uses a rolling code. I've not seen it used on an E34 but I'm happy to be corrected. The two button (grey & red) "missing corner" fobs can be easily user reprogrammed (see below).
Fobs turn up regularly on eBay for around £10 to £15, but be cautious as there are two identical types, one of which is not compatible, see here... http://www.bimmerforums.co.uk/forum...Alarm-Rogue-Fob-Conundrum?highlight=conundrum Replacement cases can be bought for £10 upwards.
The volume and number of beeps the system makes when setting & unsetting can only be programmed by a dealer or Sigma specialist.
If your fob doesn’t work check the battery first. If the LED on the fob flashes instead of being constant then the battery is on the way out. When you replace the battery clean the contacts as they get coated in a “varnish” of dried sweat and dust. The battery should be inserted positive to left, negative to right. If the battery is good and the fob LED lights up but still does nothing then it probably needs reprogramming by following these instructions (I’ll assume you have located the alarm module already)
1) Prise out the rubber bung from the remote receiver.
2) Insert a thin screwdriver into the hole and flick the coding switch to the right to set the remote receiver into “program” mode.
3) Press the red button once on each remote (max 4 remotes).
4) Flick the coding switch back to the left and replace the rubber bung.Your fobs should now work.
If there still seems to be a problem prise the remote receiver off the control unit to reset it. When you replace it (be careful you don’t bend the pins) the central locking should close & open. Re-code your fob as in steps 1 to 4.
If this doesn't work fully unplug the module, wait a minute, then reconnect it and Re-code your fob as in steps 1 to 4.
Still no joy? Prise the remote receiver off, short pins 1 & 6, then pins 1 & 8, reconnect the receiver, then Re-code your fob as in steps 1 to 4.
Finally, if all else fails prise the remote reciever off, short all the pins in the module, then Re-code your fob as in steps 1 to 4.
If that doesn't work then you need a new receiver.
User Guide (1995) is here... http://s447.photobucket.com/albums/q...e V8 1995/
User Guide (1998) is here... http://s447.photobucket.com/albums/q... V11 1998/
There also appears to be an early version of this system that has the Mk2 fobs but the remote receiver doesn't have a coding switch. If you dismantle the module you should find an orange wire. Grounding this wire to earth seems to have the same effect as flicking the coding switch, after which you follow the coding instructions as above.
Alarm Faults
If your alarm activates for no reason there are a few common faults you can look for...
1) Bonnet Pin - On older models the bonnet pin was slightly shallower so that when the bonnet was hot the pin no longer made contact due to expansion. A modified longer pin was fitted to later cars.
2) Movement Sensors - Some times these just fail and trigger false alarms. You can test this by unplugging them from the module.
3) Wiring - As the alarm is connected to the central locking system sometimes it appears to malfunction when in fact it is a wiring problem elsewhere. Most common is the wires that run from the body to the boot/tailgate through the rubber tube, see here... http://www.bimmerforums.co.uk/forum...k-what-I-found!?highlight=318is+coupe+bootlid In addition the central locking system has earths in the passenger side footwell which is prone to damp and water ingress. Make sure you check this area too as corroded earths will give similar symptoms.
4) Siren Faults - If your siren exhibits any of the following symptoms (not 2T)…
5) Low battery voltage - Most of the BMW alarm systems, including the "National Version" systems have a voltage check feature which measures the voltage at set against current voltage. If you have a battery at low charge or your car has a "drain" possibly caused by the boot wiring, then the voltage will drop over time and at some time after "set" the voltage will drop and system will activate. Remedy is to source the battery drain or to replace the failing battery.
GR40 - See 3G Mk1
2T - This is a basic siren without a key-switch. It doesn't have a backup battery.
3T - This is a basic siren without a key-switch. It has a 9.6V backup battery that can be replaced.
3G Mk1 - This is a large siren with a key-switch to override the alarm. It has a 7.2V backup battery that can be replaced.
3G Mk2 - This is a smaller siren and comes without a key-switch (Standard Siren) or with a key-switch (Emergency Current Siren). The difference is that the Emergency Current Siren monitors the electrical system and triggers the alarm if the power drops or is cut. All the components are sealed in resin and it cannot be dismantled. This is a security feature that will allow the siren to continue sounding even if you cut the wires or try to smash it.
Good Luck!
BMW E32, E34 & E36 Immobiliser and Alarm Identification & Faults Guide - GR40, 2T, 3T, 3G EWS (Sigma, Gemel, Serpi Star) EWS I, EWS II
My aim is to post all the confirmed knowledge about the immobiliser and alarm systems listed above. Many thanks to all those that have given me updates.
NOTE: There is a lot of info here so please take the time to read it carefully. If you have read the guide and still can't work out what to do then post a question in the auto electrical part of the forum mentioning that you have read the guide. Please don't add questions to the end of the guide or PM me as our private message won't help others.
If you don’t have a BMW “branded” alarm but need help then your best bet is to try a dedicated alarm forum.
Do I Have an Immobiliser? - All E34s and E36s after Sept 1993 came with a factory fitted immobiliser system. There were three types, Drive Away Protection, EWS I and EWS II. Check the sticker on the front suspension turret under the bonnet to find your manufacture date.
Drive Away Protection: 9/93 to 12/93 - The Injection/Ignition systems are disabled if the car is "Double Locked"
EWS is BMW's "Electronische Wegfahrsperre" or Electronic Immobiliser". There were two versions of EWS used on the E34 and E36...
EWS I: 1/94 to 1/95 - Improved on the Drive Away Protection by adding a starter immobilisation circuit.
EWS II: 1/95 to end of production - Improved on EWS I by adding the Key Chip and Transponder to the immobiliser circuit. New ignition keys can be bought from the dealer pre-cut and pre-programmed for £30 plus, depending on the type. You'll need to take the V5 in your name plus some ID. Expect to wait around a week.
You can also use the CODE button of the 18 button On-Board Computer (OBC) if fitted, as additional protection with any of these systems.
The EWS Technical guide can be downloaded here... http://www.bimmerforums.co.uk/forum/...1&d=1218372283
If you are experiencing starting problems and it seems like the immobiliser is activated there are a few things you can check, however if the car turns over it is not the immobiliser as the starter system is disabled when EWS I and II are activated...
1) Early E36s have a starter immobilisation relay and this can wear out
2) Also on early E36s there is an issue with poor scuttle drainage which leads to flooding of the DME (ECU) compartment, see here...
http://www.bimmerforums.co.uk/forum...creen-scuttle-drains?highlight=scuttle+drains
http://www.pelicanparts.com/bmw/tech...DME-Repair.htm
http://forums.bimmerforums.com/forum....php?p=5552421
3) All the immobiliser systems above work on a double lock/unlock signal from the driver or passenger door or a signal that mimics this from the alarm. It's always worth trying to lock & unlock the car from the passenger side (less wear on the lock) to see if it allows the car to start.
4) EWS II keys can get damaged and the chip is not be recognised by the EWS system. Try another key to see if this cures the issue. Even the grey valet key and small emergency key have chips in them.
5) Also check No.3 in the alarm faults below - bootlid wiring.
What Alarm System Do I Have? - If you don’t have a fob the easy way to identify your alarm is to find the siren or the alarm module. Generally, most BMW E36 & E34 alarms were were dealer retrofit (apart from "National Versions" see below) and were made by Sigma (part of the Gemel group). Because of this the module and siren location can vary from car to car.
In the E36 the alarm module is usually in one of three places
1) Behind glovebox in the top slot of the module carrier (most common location)
2) Under the carpet in the passenger footwell (this is a bad location as it can become damp) See here... http://www.bimmerforums.co.uk/forum...ob-to-3G-alarm?highlight=syncing+adding+alarm (4th post)
3) Under the steering wheel in the module carrier (This is more common when the system has been fitted to a pre 96 car)
In the E34 it can usually be found under the rear seat.
The siren is usually in one of three places
1) Nearside (passenger side) inner wing (most common location)
2) Offside (driver side) inner wing
3) Bulkhead near the fuse box (320/325/323/328 only)
I can't find the siren or the module! - You need to check if there is a red LED button by the gearstick and movement sensors at the top of the windscreen pillars (not on Convertible). If you don't have these either then its likely you never had an alarm fitted.
Radio Remote Control (Central Locking) - Some models had factory fit remote central locking on the key, BMW call this their Radio Remote Control (RRC) system. If you need a replacement key and your car has EWS II you'll need to get one from the dealer as above. You'll still need to re-sync the central locking to the remote yourself here... http://www.bimmerforums.co.uk/forum...mote-programming?highlight=remote+programming
"National Version" Alarm Systems - In various countries (except the USA) BMW included the option of an alarm system as a factory fit. This system is linked directly to the RRC system above, the obvious difference being the flush fit LED next to the gear selector. Another way to check is if you have a large chrome topped micro switch on the O/S/F inner wing, just near the washer bottle. This system arms and disarms through the RRC three button key and works in a similar way to the 3G systems, in that it sends a double lock pulse to set the immobiliser and monitors the door / boot / bonnet sensors for intrusion. I have not seen a version of this system with motion sensors but am happy to be corrected. The siren is located inside the O/S/F wing behind the inner wheel arch cover underneath the washer bottle. This system seems to be pretty reliable with the only reported issue being some over-sensitivity to voltage drop with cars that have an old battery.
GR40 (also known as Anti-Theft System 3) - This system was used on both the E34 and E36 from around 1990 to 1992 and uses a static code. The two button fob can be programmed by following the instructions here... http://www.abacuscaralarms.co.uk/ala...rpi-remote.htm The siren is almost identical to the 3G (Mk1). Fobs turn up regularly on eBay for around £10.
2T & 3T - These systems used on the E36 & E34 up to 1996 and have a static code. The 2T is an alarm only but the 3T is also an immobiliser. Both systems use the single button black or grey "Domino" type AC38 type fob that can only be programmed by a BMW Dealer/BMW Independent/Sigma Alarm Agent or you can buy your own programmer. Both siren types are clearly identifiable by a sticker. Fobs turn up regularly on eBay for around £10. A similar system that uses the same fob is fitted to some Subaru & Renault models and can be programmed via a plug-in keypad - This doesn't work with the BMW version as the Sigma programmer works by communicating with the module via the LED.
The 2T and 3T are not very user friendly so many replace them with 3G Mk2 or an aftermarket system. Provided the alarm is unset then it can be removed by simply cutting it out, see here... http://www.bimmerforums.co.uk/forum/threads/81929-E36-Retrofit-3G-mk2-Alarm?highlight=alarm+removal
User Guide (1995) is here...http://s447.photobucket.com/albums/q...0Guide 1995/
3G Mk1 (sometimes known as 3C) – This system was used on the E34 & E36 up to 1996 and uses a static code The black "missing corner" single button fob is only user programmable with some difficulty. You’ll need a working fob, then you need to solder and de-solder connections on the new fob circuit to match as follows (thanks to http://forum.bmw5.co.uk)....
You will need…
A working (or known to have worked) fob to copy
A replacement fob to re-programme
A decent thin tip soldering iron, solder & flux
A de-soldering tool or de-soldering braid
Open the fob and turn it over so you can see the circuit board. There is an array of 3 x 7 solder pads (see red box in the photo).
The upper and lower rows determine the 'code' for the key fob. The pads either have a blob of solder joining them, or no solder at all. You need to replicate this pattern in your replacement fob using the 4 step re-programming example sequence below.
1) The yellow dots show the code pattern for your working fob
2) The orange dots show the code pattern for your new fob pattern
3) De-solder the orange dots in the wrong position, removing all traces of solder
4) Re-solder the missing dots to match the working fob
Re-assemble the fob, replace the battery (right way round) and test. If you have made a good job of your de-soldering and soldering all should be well.
The other option is programming by a BMW Dealer/BMW Independent/Sigma Alarm Agent. Only one siren type was used (see below). Fobs turn up regularly on eBay for around £10.
The alarm module comes in two parts. The module (the large bit) and the remote receiver (the small bit).
Those familiar with the 3G Mk2 below will note that the module is identical except for the absence of the coding switch. It is possible to upgrade the 3G Mk1 to a 3G Mk2 by replacing the entire module or just the remote receiver part but you need to check the wiring is identical.
For both the above systems you may have read articles on the web that state you can program the alarm by opening the boot, closing the door, turning the ignition on 5 times, etc. These instructions are for the USA spec alarm made by Alpine and apart from giving your neighbours a laugh they won’t do anything in UK spec cars regardless of the system you have.
3G Mk2 – This Thatcham Cat 1 system came in when the E36 was facelifted in 1996 and uses a rolling code. I've not seen it used on an E34 but I'm happy to be corrected. The two button (grey & red) "missing corner" fobs can be easily user reprogrammed (see below).
Fobs turn up regularly on eBay for around £10 to £15, but be cautious as there are two identical types, one of which is not compatible, see here... http://www.bimmerforums.co.uk/forum...Alarm-Rogue-Fob-Conundrum?highlight=conundrum Replacement cases can be bought for £10 upwards.
The volume and number of beeps the system makes when setting & unsetting can only be programmed by a dealer or Sigma specialist.
If your fob doesn’t work check the battery first. If the LED on the fob flashes instead of being constant then the battery is on the way out. When you replace the battery clean the contacts as they get coated in a “varnish” of dried sweat and dust. The battery should be inserted positive to left, negative to right. If the battery is good and the fob LED lights up but still does nothing then it probably needs reprogramming by following these instructions (I’ll assume you have located the alarm module already)
1) Prise out the rubber bung from the remote receiver.
2) Insert a thin screwdriver into the hole and flick the coding switch to the right to set the remote receiver into “program” mode.
3) Press the red button once on each remote (max 4 remotes).
4) Flick the coding switch back to the left and replace the rubber bung.Your fobs should now work.
If there still seems to be a problem prise the remote receiver off the control unit to reset it. When you replace it (be careful you don’t bend the pins) the central locking should close & open. Re-code your fob as in steps 1 to 4.
If this doesn't work fully unplug the module, wait a minute, then reconnect it and Re-code your fob as in steps 1 to 4.
Still no joy? Prise the remote receiver off, short pins 1 & 6, then pins 1 & 8, reconnect the receiver, then Re-code your fob as in steps 1 to 4.
Finally, if all else fails prise the remote reciever off, short all the pins in the module, then Re-code your fob as in steps 1 to 4.
If that doesn't work then you need a new receiver.
User Guide (1995) is here... http://s447.photobucket.com/albums/q...e V8 1995/
User Guide (1998) is here... http://s447.photobucket.com/albums/q... V11 1998/
There also appears to be an early version of this system that has the Mk2 fobs but the remote receiver doesn't have a coding switch. If you dismantle the module you should find an orange wire. Grounding this wire to earth seems to have the same effect as flicking the coding switch, after which you follow the coding instructions as above.
Alarm Faults
If your alarm activates for no reason there are a few common faults you can look for...
1) Bonnet Pin - On older models the bonnet pin was slightly shallower so that when the bonnet was hot the pin no longer made contact due to expansion. A modified longer pin was fitted to later cars.
2) Movement Sensors - Some times these just fail and trigger false alarms. You can test this by unplugging them from the module.
3) Wiring - As the alarm is connected to the central locking system sometimes it appears to malfunction when in fact it is a wiring problem elsewhere. Most common is the wires that run from the body to the boot/tailgate through the rubber tube, see here... http://www.bimmerforums.co.uk/forum...k-what-I-found!?highlight=318is+coupe+bootlid In addition the central locking system has earths in the passenger side footwell which is prone to damp and water ingress. Make sure you check this area too as corroded earths will give similar symptoms.
4) Siren Faults - If your siren exhibits any of the following symptoms (not 2T)…
- No "beep" on arm & disarm
- Indicators flashing for 30 seconds to indicate a fault
- Random "squeaking" or "crackling" of the siren
- No sound from the siren (apart from when switched off!)
5) Low battery voltage - Most of the BMW alarm systems, including the "National Version" systems have a voltage check feature which measures the voltage at set against current voltage. If you have a battery at low charge or your car has a "drain" possibly caused by the boot wiring, then the voltage will drop over time and at some time after "set" the voltage will drop and system will activate. Remedy is to source the battery drain or to replace the failing battery.
GR40 - See 3G Mk1
2T - This is a basic siren without a key-switch. It doesn't have a backup battery.
3T - This is a basic siren without a key-switch. It has a 9.6V backup battery that can be replaced.
3G Mk1 - This is a large siren with a key-switch to override the alarm. It has a 7.2V backup battery that can be replaced.
3G Mk2 - This is a smaller siren and comes without a key-switch (Standard Siren) or with a key-switch (Emergency Current Siren). The difference is that the Emergency Current Siren monitors the electrical system and triggers the alarm if the power drops or is cut. All the components are sealed in resin and it cannot be dismantled. This is a security feature that will allow the siren to continue sounding even if you cut the wires or try to smash it.
Good Luck!