The waterproof thermal differential detector BS-661/A from OLYMPIA ELECTRONICS is a conventional heat detector that incorporates a temperature rate of rise detection function.

The detector triggers an alarm when the temperature reaches 57°C. Additionally, an alarm is activated when the temperature rises sharply by 32°C, regardless of the initial temperature before the rise.

The detector features a visually visible LED as well as an external LED indicator that lights continuously in the event of fire detection, until a cancellation command is given from the panel. They only turn off after a reset command from the panel.

The LED indicator briefly lights up every 7 seconds as a good operational indication.