At 3:30 am a couple days ago, the smoke detectors went off. Not the 'low battery' noise, but full alarm triggering the others to sound off as well. I checked around, and with no actual issue, pulled them all off. 6:00 visit to Home Depot. Turned off the breaker, took my meter to verify dead wires, and started replacing them, 6 total. The alarms came with wiring adaptors which were mostly fine. In 2 cases, there was already such a rat nest of wiring that I had to just use the actual wire and skip the adaptor to save space.
In this box, there was more than just connectors. And my question. Can anyone identify this? I have 3 floors, basement/first/second, and this was in the box on the first floor with a 4th connector. Other boxes had a lot of wire, but it looked pretty standard, in/out, and alarm. (And yes, crappy installation, that box is loose, but tight after putting mounting plate on.)