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Forum Index : Other Stuff : Mains powered smoke alarms are pointless.
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Gizmo Admin Group  Joined: 05/06/2004 Location: AustraliaPosts: 5078 |
I'm hoping someone can explain why we need mains powered smoke alarms. Here's the situation. Moved in a old house onto my land, and to get it certified I had to update a few things, like insulation in the ceilings, smoke alarms, etc. The smoke alarms had to be mains powered, and interconnected. I needed 3 all up, at about $80 each. I've since come to the opinion mains powered smoke alarms are ridiculous. Why? Because they need a backup battery. In fact, they wont work without one, you cant even close the case unless there is a battery in place. Take a normal $15 battery powered smoke alarm. Battery lasts about 18 months, it then screams at you at 3am to let you know its got a flat battery. You grab a ladder, unplug it off the ceiling, pop out the battery and go back to bed. Take a mains powered, interconnected smoke alarm. Battery lasts about 18 months, it then screams at you at 3am to let you know its got a flat battery, only this time its louder because all 3 smoke alarms are screaming in unison. You grab a ladder, and unplug all 3 off the ceiling and pop out the battery. Why all 3, because you dont know which one is the culprit. So whats the advantage of a mains powered smoke alarm? Anyone? This happened a couple of nights ago. Nothing like climbing up a ladder at 3 am, half asleep, dog upset, not happy. Next day I tested the batteries, one was down to 8.9v, but could still light a 15 watt bulb. It was about 18 months old, the other smoke alarms were fitted only 6 months ago, and measured around 9.2v. When these smoke alarms are due for replacement, I'll be saving a couple hundred dollars and using battery powered smoke alarms thank you very much. Glenn The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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BobD Guru  Joined: 07/12/2011 Location: AustraliaPosts: 935 |
I used to have a problem with the interconnected, mains powered smoke alarms at my previous house. Occasionally, usually at 3:00am, all of the alarms would go off. However, it was always possible to tell which one was triggered. It would be flashing the red light and it was the only one that the mute button would work on. I eventually realised that it was always the same one that triggered. The thought processes are a bit stunned when woken at 3:00am. After a bit of sleuthing, I pointed the evaporative cooling air outlet away from the smoky. Problem solved. Not all brands are hard on batteries. I used to replace the batteries about every couple of years and they were always nearly full voltage even when driving a test load. I found other uses for them until they finally died. I eventually changed to lithium batteries. The new place I'm in now has mains powered but not interconnected smoke detectors. |
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Grogster Admin Group Joined: 31/12/2012 Location: New ZealandPosts: 9306 |
I've seen both the mains ones, and wireless ones that are linked via a wireless link, but do the same thing - if one goes off, they all go off. The wireless ones are battery powered - not sure how that effects battery life, as there must be some sort of current consumption to run the receiver, but I suppose if one was specially designed to be super low power..... These days, with battery-powered smoke detectors coming with long-life 10-year Lithium batteries, I really don't see the need for mains interconnect ones. I guess the situation is as simple as: "Better the odd false alarm, then you dead from smoke inhalation or trapped by fire. False alarms: annoying, yes. HELL yes, but given the alternative, I suppose I am prepared to accept the odd middle-of-the-night battery issue. Having said that, I still don't think that is a good thing, but I guess you have to strike a happy compromise somewhere. Smoke makes things work. When the smoke gets out, it stops! |
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| BobD Guru Joined: 07/12/2011 Location: AustraliaPosts: 935 |
Glenn are you sure that your alarms were sounding for a flat battery? Mine used to give a periodic beep as an indicator of a low battery. I just checked the old documentation. Bob |
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| MOBI Guru Joined: 02/12/2012 Location: AustraliaPosts: 819 |
When I built my home about 10 years ago, I was also required to install mains/battery units although they didn't have to be inter connected. The units I used I think, were Lanson (or Quell) and had built in mains charged batteries. I installed 5 altogether and within 12 months, the charging circuitry crapped itself in all 5. I took them back to L&H only to find that they were no longer made and the replacements had ordinary 9v batteries that cut in when the power is off. As I am off grid, I don't have power failures, so the long and the short of it is that my units only ever work from my "mains". The 9v batteries last well over a year (just in case) but get replaced on winter daylight saving change over. The sad part was that the new units wouldn't plug into the mains receptacle for the rechargeable ones even though they were a replacement and made by the same company. I may as well use the Woolies brand! David M. |
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| Gizmo Admin Group Joined: 05/06/2004 Location: AustraliaPosts: 5078 |
Yeah mine are Quell, came with long life alkaline batteries. I think I'll get into the habit of replacing the batteries once a year. I just dont see ANY advantage to a mains powered smoke alarm. Just like a battery powered smoke alarm, you should replace the battery once a year, and it wont work without a battery. So whats the point of paying several times the price for a mains powered smoke alarm that offers nothing over a cheaper battery powered unit. In reality, the only difference is the mains powered version has a little green light  Maybe thats all the mains power is used for, to light the little green light?
Yet we are required to fit mains powered smoke alarms as part of a new building certification. I just dont think the people who put these rules in place took any time to actually think about it. Yeah Bob there was nothing different the night they went off. They sounded for about 3 - 5 seconds. I've left the one with the low battery unplugged, no alarms since then. I'll get another battery for it and try it out in a few days. Tempted to put a little tape over the piezo, too friggen loud! All three smoke alarms are within 6 meters of my head, one directly above the bed. The noise is so intense, you cant think and all you want to do is wack them off the ceiling with a broom to shut them up. They noise should not be painfully loud, so you can calmly assess the situation, decide to evacuate or not, and not worry about the smoke alarm noise. Glenn The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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rustyrod Senior Member  Joined: 08/11/2014 Location: AustraliaPosts: 121 |
The fire-brigade spend multi dollars every year on advertising to inform us to change our batteries on, Guess when:- "APRIL FOOLS DAY" Some of the battery shops in Toowoomba have the 9v's for a Dollar in the month of April and give you free batteries if you purchase any battery during the said month. My closest alarm is in the hall, lucky I am so deaf I can't hear it unless I 1 - am awake 2 - standing directly under it. Tests have been done, almost all children will sleep through an alarm placed 1 meter directly above them! Anyway mine don't interconnect any more, even though they all work individually.(14 yrs old) annually replaced batteries If any battery starts to fail some visitor eventually complains about the persistent "beep" every minute or so. The removed batteries are used in my multi-meters and last 'till next year Smoke detectors, mains powered, interconnected or not ARE pointless for old peoples and children Always Thinking |
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| Georgen Guru Joined: 13/09/2011 Location: AustraliaPosts: 462 |
Not sure what brand of mains connected smoke alarm I have. It flashes green light every 30 seconds when OK When battery goes weak is starts to flash red light, if we miss it for few months it starts to beep not sure how often, but often enough that I cannot sleep and have to change it. As mentioned before for some reason it always starts 2 or 3AM Sometimes I have spare 9V battery, but not always and I used to have to wear that beeping until shops open. Last time I zapped 9V battery for few seconds, few times on my 12V spare car battery and luckily it gets some charge back and alarm goes quiet. I know trying to charge non-rechargeable battery is mighty dangerous, but so far so good and battery did not explode it even didn't go warm. Suppose plus side is that there is only 3 or 4 volts difference between 9V and 12V or 13V battery. (To be on a safer side I went to garage and I wore gloves, glasses and put heavy jacket back to front to prevent myself getting splashed with debris should battery explode.) George |
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| Gizmo Admin Group Joined: 05/06/2004 Location: AustraliaPosts: 5078 |
Came home at lunch time to find all three smoke alarms going off. No smoke or nothing. Trying to find a ladder, tripping over the dog, ended up smashing one off the ceiling because it wouldn't unclip, and threw it across the room. The other two alarms went quiet for a minute, then started again. All three are now in pieces. All batteries are less than 6 months old and measure over 9v. I am smoke alarm free! Glenn The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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| rustyrod Senior Member Joined: 08/11/2014 Location: AustraliaPosts: 121 |
Now that you have sorted out your smoke alarms, that reminds me I MUST experiment with mine. They are interconnected BUT BUT, if I trigger one in test, the others do not go off in symphony/cacophony. I should pull them all down and connect them with a shorter wires and try them. Seems a big job as I can't hear them anyway! Perhaps to see if they will detect burning - - I may set them alight? 
I have had no trouble with the one that is still in it's delivery box some where on the floor. 
Always Thinking |
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Tinker Guru Joined: 07/11/2007 Location: AustraliaPosts: 1904 |
There are 3 smoke alarms in my place. One of them likes to go off with high humidity, the other two are unaffected by it. I'll have to remember putting the battery back in, now that the weather is drier. They do strange things it appears. Klaus |
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| Gizmo Admin Group Joined: 05/06/2004 Location: AustraliaPosts: 5078 |
Its not hard to understand why so many smoke alarms are left in a non working state, with the battery removed, etc. Thing is, these annoyances could be easily fixed by the manufacturer. For example, if the battery is low, make sure we have daylight before beeping. If you press up on the smoke alarm, or shine a torch at it, its shuts up. And some way to adjust the volume, I'm a light sleeper, I dont need to be put in a state of panic by excessive noise. I wonder how many people have fallen off a ladder while there were half asleep trying to shut up a rogue fire alarm. And I think the interconnecting of alarms is not a good idea, makes it impossible to work out where the source of the alarm is coming from. I found a old battery smoke alarm, put it in the hallway, it will do for now. Will replace the mains powered smoke alarms next week with some battery smoke alarms, not interconnected. Glenn The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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raymond thomson Newbie  Joined: 19/09/2013 Location: AustraliaPosts: 36 |
Cracked it! - maybe. Yet another 2:00am smoke alarm (false) and ladders in the night. Here in sub-tropical Queensland we often get swarms of very tiny bugs that defeat the flyscreens. Reading by bed-side light becomes impossible for a few days. The little green beacon on the smoke alarm that helps navigate across the lounge room on very dark nights also attracts these bugs. On checking out the alarm it is full of dust and dead bugs and after a blow out resumes normal operation until the next time. Interestingly the alarm with the red LED, different brand, does not have false alarms but I have not checked to see if there is an accumulation of bugs. May have to paint over the green LED. Raymond. |
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| paceman Guru Joined: 07/10/2011 Location: AustraliaPosts: 1329 |
It might be that green light is getting close to wavelengths that bugs like, i.e. on the UV end. That's why bug zappers use UV tubes, to attract the bugs to them. If the LED's were changed to red ones it might help because red is at the opposite end of the spectrum. You'd also probably need to limit the current more though because of the much higher output of red LEDs - otherwise you might be awake all night anyway.  |
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| domwild Guru Joined: 16/12/2005 Location: AustraliaPosts: 873 |
Once I sell my house I will have to put in smoke alarms. Schnapp is selling non-mains ones, where the battery is supposed to last 10 years? May buy them and install them and see if I can get away with them. One side of the house uses asbestos roofing, so I may claim no electrician wants to work there, the other side has a high ceiling without a crawl space. How would an electrician install them there, do they grab the mains from a light nearby? Is the lack of a crawl space a valid excuse?? Taxation as a means of achieving prosperity is like a man standing inside a bucket trying to lift himself up. Winston Churchill |
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| Phil23 Guru Joined: 27/03/2016 Location: AustraliaPosts: 1664 |
Didn't enjoy this thread last night. Recently replace the last of the cloth wiring in this old joint while adding my heating ducts. Added 2 new 9V dual sensor smoke detectors from Bunnings, and to be really thorough, while playing with wires, decided to also add a couple of mains powered ones. One in the ceiling space, and the 2nd in the house, interconnected, to make sure that there is no chance of the ceiling space one not being heard, or dismissed as something else. Someone PLEASE tell me that these ones aren't prone to false alarms..... I don't want to be repeating Glenn's 3:00am escapades into the roof on the -5°C nights. The 10 year battery is an interesting concept. That one particularly amuses me when I'm standing in the isle looking at all the detectors hanging on the peg board & hearing the low battery chirp coming from an unidentifiable few. Commented to a "Team Member" on the chirpy ones, His reply, "Grrr, I've been trying to work out which ones for weeks". Cheers Phil. |
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| Grogster Admin Group Joined: 31/12/2012 Location: New ZealandPosts: 9306 |
I had to replace one of those Quell ones last week. Pipping for no reason. Replaced battery, still pipping. Sets off the others in the house with pips too. Checked all three to be sure we did not have a flat battery hiding in one of the others causing the problem - all batteries healthy 9v. Finally decided to replace the suspect one as it was slightly more discoloured then the others, and would start screaming(and set the others off too) as soon as the mains was applied, so I was suspecting a PSU fault with that unit. So far, no reported problems - but it is the weekend.... I totally agree with Gizmo - the mains powered ones are a really stupid idea for the reasons he laid out. That is only me agreeing with him. Others may see the merit of interconnected mains detectors, but I am not one of those.  Smoke makes things work. When the smoke gets out, it stops! |
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| Georgen Guru Joined: 13/09/2011 Location: AustraliaPosts: 462 |
Dual powered, mains with battery backup would be probably not bad idea. Possibly with rechargeable batteries to reduce longer term cost. Also, with current technology we could have smoke alarm with little display screen that when activated, could tell about status of unit, on top of usual alarm when things go out of order. George |
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| Gizmo Admin Group Joined: 05/06/2004 Location: AustraliaPosts: 5078 |
Mains powered are pointless, just buy battery powered smoke alarms. There is no advantage to mains powered smoke alarms, you still need to replace the battery every year. The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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