For magnetic, you could use the following Magnetic sensor placed above the track in front of the robot to detect the presence of absence of the track.
If you can have some kind of wall at the end of the track, you could put an ultrasonic sensor to detect the distance between the robot and the wall and start braking a some point. Ultrasonic sensors have more range than the magnetic sensors, so it could give you more time to slow down.
Sensors won’t work directly with the SyRen. They should connect to your electronics that controls the Syren. It could be an Arduino, a Raspberry pi or any other controller.
In that case, you will need to add some intelligence to you design in order to use sensors. Otherwise, your only option is pretty much using mechanical limit switches to cut the power which is not excellent if you want the robot to continue to function.
