The safety chain is a series of contacts in series monitored by the electronic lift maneuver card. If only one opens, this will cause a cut in the safety chain, which will be detected by the card and considered as a fault.
Before the order to start the engine is given, the information passes through a multitude of contacts which must all be "closed", thus proving that all the safety devices are good, and that the elevator is ready to go.
The safety chain begins with the most important contacts, such as the speed limiter, traction control, the limit switch system, locking of the cabin doors, etc.
Thanks to the information concerning the security chain, our technician already knows where to look when he arrives on site. In this case, he notices that the wire of the toe-guard plates is cut. This contactor is connected to the security chain, which explains why it was spotted. A simple repair will make it possible to restart the elevator in a few minutes.