I have a smoke alarm that's not working. It's hardwired interconnected 4 wire detector. I cant find one near me and I have a state inspection on Tuesday. Can I wire a three wire detector to it? Dumb question maybe but I have no clue. It has 2 reds and two blacks. These things are on year eight so I'll be replacing them all this summer but I need it working by Tuesday. LOL. They all worked 7 weeks ago when I scheduled the inspection but had a monthly drill today and one quit working. I can have a replacement on Thursday but sure hate to wait another 7 weeks for an inspection. It'll work or it won't I guess. Thanks.

Are you wired into a central alarm panel? If device goes off it gives a location? Or are the hard wired for power and are a stand alone? If stand alone and you are looking for power then wire in a three wire device. But if you are wired into a fire panel or annunciator. Then you will need the 4 wire kind. Hope this helps. Not sure what your code is. But NFA code is. You need to replace device how old device was previously

4 wire, 2 blacks and 2 reds, you have a supervised smoke detector system with an end line resistor somewhere in the system. Probably 24v DC. This is not the residential kind (you buy at the Home Depot) that have 3 wires, (hot120v-neutral-interconnect).
If I was you I'd get a fire alarm company out there to see what you've got. They could find a compatible replacement easy enough.
What brand system is it? Are the heads addressable?