Richard Tacy

I've purchased a 1987 560 SEC and when I open the door I hear a LOUD ticking,LIKE A CLOCK. It comes from beneath the passenger's side floorboard. My mechanic says it may be part of a security system, which is activated by a "RED DOT" key. I went to a Mercedes dealer to get such a key and was told they haven't been around for years.
Any ideas?