Sensors for electronic article surveillance (EAS) have meanwhile become a mass application for amorphous soft magnetic materials. The talk surveys the most wide-spread EAS systems with particular focus on the physics behind the tiny sensor strips. Basically all EAS systems operate on the same principle: Articles are affixed with security labels which, if not deactivated at the cash register, respond to electromagnetic fields generated from pedestals at the store's exits. The response is picked up by an antenna in the pedestals, thereby triggering an alarm. Magnetic security labels consist of a thin soft magnetic strip, mostly an amorphous alloy, which acts as the sensor and a semi-hard magnetic material for activation and deactivation purposes. By matching its dimensions, chemical composition and thermal treatment, the soft magnetic material is given a specifically designed magnetization behaviour. The latter is evaluated by the detection electronics in order to distinguish the label from most other possible magnetic objects passing through the interrogation zone. The focus of the talk is on acousto-magnetic markers which are representing the latest technology. They are based on magneto-elastic effects. The sensor strip is excited by magnetic field pulses to longitudinal, resonant vibrations. Once such an exciting field pulse is over, the vibrations ring down in a characteristic way which provides a unique signal in order to identify the label.