A method for producing a hook-flash event on a loop (6B) incorporating a supervisory signal circuit. The supervisory signal circuit includes a supervisory signal source (2) that causes a supervisory current to flow around the loop through a threshhold detector device (4) and one or more supervised devices (10 and 24). When a counter-signal source (34) is connected to the loop, it opposes the flow of loop supervisory loop current (12), causing its level to drop below the detection threshhold of the threshhold detector device. After a timed period, the counter-signal source is disconnected from the loop, allowing the level of supervisory loop current to return to its normal state, thereby completing the hook-flash event on the loop.