You should actually never test a smoke detector that way, can get soot on the sensor and degrade its accuracy. Instead use a product like this https://www.amazon.com/CRC-2105-Liquid-Detector-Aerosol/dp/B07BTJWL6P/ref=sr_1_2?ie=UTF8&qid=1523491451&sr=8-2&keywords=smoke+detector+tester+spray