Cheap smoke detectors are pretty much all optical these days, and even the unbranded £2 Chinese ones have pretty sophisticated self-tests: https://www.youtube.c

Cheap smoke detectors are pretty much all optical these days, and even the unbranded £2 Chinese ones have pretty sophisticated self-tests: https://www.youtube.com/watch?v=uzKAZCKjpU8 https://www.youtube.com/watch?v=uzKAZCKjpU8 To be honest, I'm not sure whether there's even any point having expiration dates on modern photoelectric detectors, except as a way to sell more smoke alarms.