Smoke Check is a proprietary hydrocarbon blend that works by simulating the chemical makeup of real smoke. This product was designed and introduced in 1979. It is the original aerosol smoke detector test spray. Smoke Check™ is UL/ULC listed, FM approved, is complaint with NFPA 72 codes and standards, and is approved by virtually all smoke detector manufacturers. This patented product leaves no residue, is 100% ozone friendly and is proven to be safe when used as directed. The active ingredient of our smoke products is used in most household cosmetics. "Pushing the Button" only test the power supply, using 25S Smoke Check test the sensor and power supply, in one simple step.