Delta Photoelectric Smoke Alarm

Delta Phtotoelectric Smoke Alarm not working – Waste of time. Do not buy. Product doesn't have a link to the instruction manual and doesn't work Tried this alarm already 3-4 time before throw away. Each time did not find it useful. Just now decieded to test. The battery installed as in instruction duracel 9v. Long press the battery it makes noise. Seems all good. Bring to bedroom, attach to the ceiling. in the hallway behind the corner I have old alarm. In the hallway I closed door into all room. The only far away doors into the kitchen and living room were opened, but that's far away. So I take heat gun and wooden stick and start siting in the bedroom heating that stick with heat gun. After 5 minutes in the hallway alarm started making noise but that one in the bedroom did nothing. I'm not sure if that thing works at all.