Door lock beep
 

When I use my remote to lock my car, the horn now chirps.

I had an aftermarket stereo installed a couple of days ago and I do not recall it doing this before the stereo was installed.

Does the beep or chirp indicate that the alarm is not active, or what?

There is an alarm contact. This contact does not make contact with the body of the radio because the body has a plastic insulator. On the 220 car it is on the left side, so when we put in an aftermarket radio we put a piece of tape on the body to act as an insulator.

On the 210 I think the insulator is on top.

Some people unplug the wire to the contact and then cover the end with tape so it will not touch metal. Then you will not get a beep.

Even with the beep the alarm system still work. The beep is to let you know something is wrong with the system.

Check a few things:

Your center console, front and rear trunks. If they are not closed all the way until you hear the latch click it causes the beep. Make sure the console is not stuffed with things to the point were it does not latch.
:cheers:

I told ya so!
 

This was something I mentioned in your other post when you were going to install the head unit....On my 210 there was a tab with a plastic sheath around it which connects to the mounting sleeve.....Mine was on the bottom right as you look into the dash......You have to tape it up and tuck it away so it doesn't make contact with any metal, or your alarm system will give you a false reading......