When the smoke alarm reckons the battery is dead, I take it for my projects...
Yeah, yeah, I know it only powers my project for a couple minutes, but I can't waste them...
Amazon.com: Rechargeable 9V Batteries, SHENMZ 9V Battery 9Volt 1300mAh USB Charging Cable
These are ok for tiny projects and they last a full year in the smoke alarms.
The ones I currently have are 7 years old and still doing well.
Hi,
I doubt 1300mAh 9V in that package with 5V USB charging socket on the bottom.
How would they pack it all in?
Tom... 
When you squeeze them for that last electron then . . .
When you see a 9v battery with the layers exposed, you understand the shape of a battery schematic symbol (alternating long & short lines, stacked in a pile - Volta's Pile they called it)
I had that. Very painful.
Coulda been worse, coulda been Gomer's Pyle!
Italian word for enema: innuendo
I've had diverticulitis, don't get me started on proctology jokes!
(Waiter! Check please!)
Look what I just found!!
I've never seen those before, interesting and handy for Arduino Projects.
Not suitable for smoke alarms I'm afraid. Brand new, alkaline type only. No nickel metal, no carbon zinc, no lithium ion that requires the user to recharge. There are new lithium ion types that are marketed as good for 10 years but they are designed for this type of battery. If you are using lithium ion batteries in a typical smoke alarm that was designed for replaceable alkaline batteries, you risk the smoke alarm not providing the warning chirps that notify you if the battery needs replaced, since the batteries die very suddenly compared to alkaline batteries and that warning time frame may be dangerously reduced. In other words, you may have a dead battery in the device and not know it.
Also the same for battery powered keypad door locks. It's ill advised to use lithium ion batteries in those for the same reason (but doesn't defeat the UL certification of the device as in a life safety device such as a battery powered smoke alarm).
Your local fire codes may vary. Just a bit of public information folks should be aware of, since it bears on the discussion. I can't stress enough the absolute value of the correct number of correctly working smoke alarms in terms of saving lives in fires. More than any other factor by a massive margin, smoke alarms are the thing that will determine whether or not folks survive a house fire if they are home when the fire occurs.
Also, the old "one alarm for each level of the home" is not enough. Every bedroom should have its own as well (especially if you sleep with the door closed) ideally interconnected but this retrofit may be impossible for older homes. Also, your shop/lab/workspace/garage should have one.
https://www.nfpa.org/Public-Education/Staying-safe/Safety-equipment/Smoke-alarms
I was told a heat detector is preferred for a garage due to dust and such that may be present there.
Interesting product - the USB charging port is for charging the 9V battery.
Another similar product is rated No. 2 here. These mantain 75% charge for 3 years - great for smoke alarms.
Especially if the garage is attached to the house or in close proximity, choose an ionizing model of smoke alarm instead of a photoelectric type to help prevent false alarms in such environments where more than usual dust may be present. If there's heat, there's already fire. Heat detectors aren't intended to protect lives but to either (a) reduce property damage or (b) act as a triggering device for a fire suppression system such as sprinklers. Vacuum out the smoke alarm periodically and . Even better, a combination unit placed in a well thought out area of the garage (since many garage fires start out as slow smoldering type, better suited for photoelectric smoke detection) where good housekeeping is practiced is the best way to minimize the risk to your family from fire.
Would you rather have false alarms from time to time or a garage fire?
@hallowed31 are you an FPE?
I work in the fire service. Some of my roles involve public education. troubleshooting, installation, inspection and maintenance of fire safety equipment
This is only true sometimes. In Australia, smoke alarms must be hardwired, and have a battery.
The reason they are hardwired, is that when the battery is dead it will still alarm to warn you to replace the battery. And the NSW Fire service recommends using Lithium ion batteries. But I suppose that would be different in every country.
How does that work when I am grinding metal on my linisher??
As I said previously, local codes may vary. Also, hardwired alarms are not always possible in much older homes. In Ontario, Canada, what you are saying is true but that's a Building Code requirement for new construction (also every bedroom, and strobing) not specifically one in the Fire Code for all single family dwellings.
Good question; I don't know. Heat detectors are not life safety equipment in residential applications. Here's what Honeywell says:
https://buildings.honeywell.com/us/en/news-events/news/2018/05/heat-detectors-vs-smoke-detectors-whats-the-difference#:~:text=In%20a%20nutshell%2C%20here's%20the,the%20development%20of%20a%20fire.
Can a modern heat detector, wired in with the residence area smoke detectors, be swapped out for a smoke detector?
They're there.