SPL-TO is an optical tamper sensor that detects any attempt to dampen the piezoelectric transducer of the siren by using PUR foam.
The principle of operation of the sensor is similar to that of the infrared barrier. A transmitting element and a receiving element are installed on the electronics board, with infrared pulsed beam being transmitted between the elements. If the transmission is disrupted by an obstacle, which may be the expanding assembly foam, the sensor opens contacts of the relay, thus triggering an alarm.

detects an attempt of damping the siren with acoustical signaling with PUR foam
works with: SPL-2030, SPL-5010, SPL-5020