central locking alarm problem E320 yr 2000

This used to happen intermittently but now almost all the time.
When I lock the car with the electronic tab everything locks ok but
after a couple of seconds the direction indicator lights start flashing again and the car remains like this.
Whether it is a central locking problem or whether it is an alarm problem, I do not know.
There are two kinds of alarm sensor in this standard model: a tilt sensor to detect if the vehicle is being hitched to a tow truck, and an ultrasound sensor to detect is somebody breaks in. I can disable either or both of these with a rocker switch. However disabling the alarm sensors does not stop the problem.
It is an unacceptable problem because leaving the lights flashing will discharge the battery and leaving the car unlocked will invite thieves.
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