> Smoke detectors usually have replaceable batteries though, which kind of work like an off switch.
That is changing. Several states, including California and New York, no longer allow replaceable battery smoke alarms. They require long life sealed batteries. Other states are in the midst of doing so.
They are doing this because smoke detectors have a limited lifetime. You are supposed to replace them 10 years after manufacture. However, they don't suddenly stop working at 10 years...they just get less and less effective over time.
Many people don't realize they are supposed to replace them, or know it but forget. I didn't know, for instance, until mine was ~17 years old. It still went off when I'd sear a steak if I forgot to close the door between the kitchen and the room it was in so there was no obvious thing to tell me that it was likely losing effectiveness.
By going to units with a sealed battery meant to last the lifetime of the unit they hope to make it more likely that people will remember to replace them. When it is time the units will beep like the replaceable battery units do when the battery is getting low.
I would guess there are also people with the replaceable battery units who when it starts signaling low battery take out the battery planning to pick up a new one next time they are shopping, forget, and take a long time to remember if ever. Sealed units will help there, too.
BTW, when buying smoke alarms it is probably best to avoid Kidde (also avoid them for fire extinguishers). They are prominently featured at Home Depot and Walmart, and can be a little hard to avoid if you don't take a bit of care. Here's why to avoid them, from the Wirecutter.com article on basic smoke detectors:
> With placement on the shelves of Home Depot, Kidde is the most prominent competitor to First Alert, but its overall track record is, in a word, disturbing. In 2018, the company recalled more than 450,000 dual-sensor smoke alarms; in 2016, it recalled 3.6 million smoke/CO alarms, and in 2014, it recalled 1.2 million smoke/CO alarms. In addition, since 2005, Kidde has enacted three separate fire extinguisher recalls of 470,000 units (2005), 4.6 million units (2015), and 40 million units (2017). Worst of all, in early 2021, a federal judge ordered Kidde to pay a $12 million civil penalty “in connection with allegations that the company failed to timely inform the Consumer Product Safety Commission (CPSC) about problems with fire extinguishers manufactured by the company.” For these reasons, we can’t, in good conscience, recommend any Kidde products to our readers.
> Although First Alert is not immune to recalls (it recalled nearly 150,000 smoke alarms in 2006 and roughly 600,000 fire extinguishers in 2000), none of them are recent or on the scale of what Kidde has had to do.