A timed break in the local loop circuit that signals the switching equipment without dropping the call. Pressing the receiver button or a dedicated flash key briefly opens the circuit, typically for 300 to 1000 milliseconds. Central offices and private branch exchanges interpret this specific duration as a command to activate features like call waiting, three-way calling, or call transfer.
Heard on the job
Tell the customer to hit the flash key once to switch over to the second call, because a long hook flash will just hang up on both of them.
Insider tip
The timing is critical. If the break is too short, the switch ignores it as line noise; if it exceeds one second, the switch interprets it as a disconnect and drops the call.
Also heard as
- flash
- switchhook flash