The smoke detector is mandated by legislation in a lot of places. The premise being it can break, you don't know, and thus die.

Not a fan of LEDs, but I at least understand why this as it is.

I had the tenant before me install fake fire detectors once. Always a green flash every few seconds but that was the only electronics in there. I only noticed because after a few years, I never had to change the batteries, so I decided to check them.

When you move into a new place, always check they are real and work.