Lost in the jungle hundreds of smoke detectors exposed in supermarkets, sometimes completely unknown brands, I decided to find out more on the net and to direct me to a proven brand, offering a model for a suggested average price (around 30 to 35). Instructions in French, comes with 3 AA batteries, mounting bracket. Testing with the test button successful. A shrill beep sounds. It must be tested regularly. If the beeps repeatedly, the signal indicating that the battery change is needed. If warning light comes on for you to direct you in the dark if a power failure occurs.
Delivered within a week. Nothing more to say, except that I hope to never hear that thing go off ....