Invaders are sure to make a run for it if an alarm or bright light suddenly fills the house. That’s where the Samsung SmartThings Motion Sensor comes in: compatible with the SmartThings Hub (also under $100) you can program the practically unnoticeable sensor to detect and report unusual movement when you’re asleep or away. You can also set it to trigger different results as response, like turning on the lights or setting off other electronics. As soon as your house springs to life, you can rest assured that any uninvited guests will scram—and think twice about targeting your home again. Available on Amazon; $40.