The DIVERSITECH Tattle-Tale Control Monitor (3 Pack) is a disposable, pocket-sized device designed to quickly identify open controls in response to a malfunction. Ideal for monitoring safety controls, fuses, overload relays, and more, this simple-to-use tool saves time by eliminating the need to trace safety control shutdowns, even if intermittent. Perfect for HVAC technicians and electricians, the Tattle-Tale Monitor provides efficient troubleshooting and enhances safety. Please note: Not for use with lockout relays; use TC-007 instead.