ZAPSTR (Zonex Air Proving Switch with Timer and Relay) is a simple, reliable way to interlock a booster fan with a laundry dryer or other air moving device. The ZAPSTR senses positive air pressure in the duct, then triggers a relay to activate the desired device. It runs on a timer for ten minutes, then checks to see if positive pressure is still present. If there’s pressure, it runs again, if not, it shuts off the device.