What are these old smoke detectors worth?

Fyrnetics Lifesaver Model 0908 Smoke Alarm with Hush Control and Safety Light
Pittway / First Alert Smoke Alarm Model SA76RC
1990 Pittway / First Alert Smoke Alarm Marked Model SA81D On BOX and marked 83R On Dectector
1984 First Alert SA80FCSmoke Alarm

I can’t give you anything exact but those are all very rare: just the same though collectors don’t have all the money in the world, so please be moderate when you price them.

You can always donate them to various fire museums if no one buys them on eBay.