How long can alarms last with disconnected Mains power?

[stroller133]

We recently moved into a house with an alarm installed , but told by previous owner it hasn't worked for years. We had an electrical safety test and initially failed and the alarm appeared to be the cause. I agreed to have the alarm removed from the mains and have my certificate now. No loss as alarm is not in use.
However about 4 hours later the external siren came on, probably for about 30 minutes continuously and then stopped. How long can the battery power the siren? I'm concerned it could sound again in the middle of the night.

I'm also a bit concerned the PIR sensors are still lighting up?

 

[stem]

There are two batteries involved, a large one inside the control panel that keeps the alarm powered up during a power cut. Normally they will last longer than 4 hours, but if it's elderly, I suppose 4 hours would not be unusual.

When this battery becomes discharged, all power is lost to the alarm control panel. At this point, as far as the siren is concerned this would be commensurate with a 'would be burglar' cutting the cable to the siren and when that happens, a second smaller battery inside the siren which is designed to trigger the alarm in such an event, will sound the alarm for either a pre-set time, or until the second battery becomes discharged.

If the siren battery is now completely discharged, then it won't sound again. If the siren is controlled by a pre-set time and the battery hasn't discharged, it will continue to power the siren circuity which should prevent it from resounding and will of course eventually discharge. What happens then? is the question. Depending upon the circuitry and the level of power the siren needs to operate, there might be just enough power left for it to make some sound..... or not.....

I'm only familiar with a couple of types of alarm, and unfortunately the sounders and panels are not necessarily paired up the same on every installation, but if you could provide details of the make / model of the control panel and a photo of the siren, you may get lucky and someone might recognise it and be able to give you a definite answer.

 

[stroller133]

I think the internal one is now dead as the keypad lights are no longer lit. I suspect neither battery had been maintained in the last 16 years so hopefully they will quickly drain. The alarm is an accenta 8 mini and external box is white with a blue strip light at bottom but can't see any name.

 

[secureiam]

Firstly to determine how long a battery will last will depend on its size its condition (current capacity), and the system draw.

Battery life can vary and for lead acid batteries 4/5 years is what is worked to but should be tested annually to determine its condition.

The mini can take a max 2.1/2.3 Ah battery the draw in standby is relatively low but is based on the panel bell and devices attached to it.

Most modern bells have a cut off that is set for 15 minutes, when the internal battery failed, no power to the main bell and it was then triggered.

You should remove the battery from the system and if the mains isn't connected the bellbox it is unlikely to trigger again.

 

[Gibbies]

I think the internal one is now dead as the keypad lights are no longer lit. I suspect neither battery had been maintained in the last 16 years so hopefully they will quickly drain. The alarm is an accenta 8 mini and external box is white with a blue strip light at bottom but can't see any name.

After 16 years best to change the siren to keep an up to date modern appearance.

 

[secureiam]

After 16 years best to change the siren to keep an up to date modern appearance.

well a good clean of the cover, or swap of the cover if its still okay, although some fall apart.

 

[Gibbies]

well a good clean of the cover, or swap of the cover if its still okay, although some fall apart.

Siren replacement during a maintenance visit approx £75?? Gotta be worth having new imo. 16 year old siren that has tamper switches exposed to extreme weather just not worth the gamble.

 

[secureiam]

Certainly is, but people like to gamble apparently