There was a thing like 10-20 years ago about "LED Throwies". The idea is that they were really cheap, used a coin cell battery and some magnets and led's. You soldier them all together then toss them up in random places and they would glow at night for however long the battery lasted.
Now, it should be cheap as fuck to make something similar but just as a "chirp throwie" and do the same thing... That would be fun.
I can see the headlines now: The Newest Face of White Supremacy: the fire alarm chrip
Before Thinkgeek was bought out by Gamestop they sold a product call the annoy-a-tron which was exactly that. It chirped every few minutes randomly and you could stick it anywhere with a magnet.
Yeah, you can still get that stuff all over the place. There was one called an "evil tron" that made creepy sounds instead. I was thinking some little DIY thing with a tiny capacitor and solar cell or something to keep it going long term. Should be cheap as hell to build.