How do anti-static wrist strap alarms detect a disconnection of the wrist wrap?
The automatic monitoring straps that I have used have two electrical connections in the strap. The strap has a mini plug (3.5 mm?) on the end of the cable so both connections can be made to the sensor. The strap is electrically built in two isolated pieces, the metal ones had two 180 degree halves. If the monitoring device didn't detect some resistance in the person's skin, it would sound an alarm. We often had to use a special cream on our wrists to get a good enough connection. Each signal had a 1M resistor in the plug for safety.