Black, about the size of a cigarette pack, it's the lock controller for your entry and bay locks, and receives wireless remote input. It can be reset if your remotes or entry code panel have programming faults.
Also in that cubby, just for future relevance, you should find a steel plate with a push switch and a couple other devices "mounted" on it. The push switch is for techs to check your ABS system, and the probably loosely mounted clear cylindrical device is your signal flasher.
Joel