The door stays open for n amount of time (normally around 1min but I changed it to 30sec). The drive has a laser sensor attached to it (it is required to have installed with automatic doors in Switzerland if you don't want any issue with insurance). As soon as the specified amount of time has passed, the door drive tries to close the door. It only works if the laser sensor detects no obstacles.

Maybe a bit off-topic but: The only thing that differs an "fire-protection approved" door drive from a non approved drive is that the drive is not allowed to have an option to keep the door open. Also in case of power outage (or fire) the door needs to close without power.