Integra-Signum is a Swiss train protection system introduced in 1933. Originally it was called Signum; the name Integra was added later. It transmits data inductively and is simple, robust and reliable also in snow.

The locomotives have three sending and receiving magnets and there are two trackside magnets near the signals.

Integra-Signum requires the train driver to confirm distant signals that show stop and distant or home signals that show caution. If no confirmation is received or a home signal that shows stop is passed without authority, the train is stopped automatically. This is achieved by interrupting the power supply to the motors and applying the emergency brake.

The locomotive's sending magnet is a strong permanent magnet, which induces a current in the receiving magnet in the middle of the track, if the signal's short-circuit contact is closed. The receiving magnet on the locomotive consists of two magnet field detectors, which detect the signal's state according to polarity and timing of the magnetic field emitted by the second magnet outside the track:

Stop (home signals): positive - negative, concurrent

Caution (distant signals): negative - positive, concurrent

Caution (home signal): positive - positive, not concurrent

Because Integra-Signum can only stop a train when it's "too late", i.e. after the red signal, it is not sufficient if there is an obstacle less than the braking distance away from the signal, which is especially a problem with fast trains. To address this issue, Zugbeeinflussung ZUB has been introduced.