Your Nest Protect should last five years. That’s pretty short, considering that you should change your smoke alarm every ten years. Essentially, you’ll have to replace this detector twice as often as you would with a standard device. Check in periodically to make sure your Nest Protect still works. If it needs replacing, you want to know before a fire or other incident. There are three different features that test the device: Self Test: Automatically checks whether the device has power and its sensors work. Sound Check: Automatically Tests speakers/siren and horn. Safety Checkup: Manually tests all of the above.