Inside of the dispenser, a ceramic piezo disc vibrates as electricity passes through. This propels the ultra fine TEMPO REFILL particles into the room. The particles are only one micron in size and will stay airborne up to two hours. The TRIPLE S TEMPO AIR CARE SYSTEM uses safer chemical formulations than traditional aerosol sprays, with lower, no added VOCs, no metal cans, refills are recyclable, no isobutane or acetone. Indicator light blinks green when operating; red when refill needs replacement; and it goes completely dark when you need to replace the batteries (3 AA). Choose from four indulgent fragrances that last up to 90 days.