What is a Collapsing Circuit?

A 'collapsing circuit' - in its idea - is a circuit designed to detect a failure in a circuit and act on it. The most basic implementation would be to monitor voltage/amperage levels on the target circuit and react when those levels change (a wire is cut, an element wears out etc.).

Collapsing circuits are used in electronic security devices like alarms (alarm is set off if tampering in the device is detected), and bombs (the load is detonated when, for example, the counter is disconnected).

Typical (generic) usage for such circuits is mainly intrusion detection and failover systems - a collapsing circuit could be used to warn the user of a failure, or to enable a backup system.

One would do good to distinguish between physical (ie. electronical) and logical (signal-based, software) 'collapsing circuits'.