This unit positively lets you know every remote flash fired, every time. Stick a cordless TeleFlash onto each flash in your setup (or clip it to the flash cord for better visibility). TeleFlash detects the electro-magnetic surge of a "good" flash firing, blinks a bright red LED for 5-10 seconds, then automatically resets for the next shot. A quick glance at each TeleFlash in your studio gives you instant, reliable flash confirmation. A single 9V battery (not included) provides power for thousands of activations.