The photoelectric sensor is better suited at detecting larger particles usually from smouldering fires, that don’t erupt immediately into flames by using a light beam inside the detector which doesn’t directly hit the sensor, but will do so in case smoke enters the device and forces the light towards the sensor. Besides the smoke detecting sensor, the First Alert 2 in 1 also has a Carbon Monoxide Electrochemical sensor which has the role of detecting any rising levels of CO inside the room and triggering the alarm when the concentration crosses the safety levels there will be both visual and audible signals – up to 85dB at around 10 feet. If the sensor detects increasing levels of Carbon Monoxide, the CO LED will flash a red colour and the audible alarms will have the following pattern: four beeps, then pause, four beeps and then pause. Otherwise, if the sensor detects smoke in the room, the Power/Smoke LED will flash a red colour, while the audible alarm will beep three times, pause and again three beeps and pause. You can silence any of the alarms by pressing the Test/Silence button: if the smoke alarm has been silenced, then it will remain silent for about 15 minutes before reactivating if the smoke has not been cleared; if the CO alarm has been silenced, it will remain silent for up to 4 minutes before reactivating again if the CO levels haven’t decreased. Now, let’s get to the smart part of this smoke/CO detector.