IanM_

This has been going on for a couple months, my 2013 C300 just randomly beeps throughout the night, I've changed the batteries in both key fobs and replaced the car battery itself, yet the mystery beeping continues. I can't seem to find a single case of this reported anywhere else on the internet. What am I missing?

I should have added, I have nothing aftermarket installed on the car, just standard alarm, radio, everything. (boring, I know)

alecmascot

The alarm siren batteries are probably corroded.
In the LH wheel arch.

MBENZTECH

Did you get any of the keys wet?? Try taking the batteries out of the key fob and leaving them out. If the issue stops, then one of your keys is sending random signals. If it doesn't stop the issue, then check for water ingression in passenger compartment.