Perhaps the most important thing we learned from our testing is that smoke detectors have a limited range, which is one of the reasons modern building codes require a unit in every bedroom as well as in areas adjacent to bedrooms. To test effectiveness, we sprayed test smoke from an aerosol can directly at each device and timed how long it took the alarm to sound. We sprayed the test smoke from 5, 10 and 15 feet away. Every detector sounded within 30 seconds at the 5 foot mark. Three smart smoke alarms –Nest Protect, Halo+ and First Alert Onelink – went off at the 10 foot mark. All but one of the smoke detectors, the Nest Protect, failed to detect dangerous levels of smoke at the 15 foot mark. How Much do Smart Smoke Detectors Cost?Always weigh the costs against the benefits you might get from a smart smoke alarm. On average, you can expect most smart smoke detectors to cost around $100, though some units cost as much as $250, which can be up to 10 times more expensive than normal units. This can make replacing all of the existing smoke detectors in your home very expensive. To keep costs down, consider using traditional units throughout your home with smart smoke detectors in main areas. Traditional smoke detectors typically cost between $10 and $40.