Infrasound

Cocoon Is a Smart Home Security Device That Uses Infrasonic Sound to Detect Intruder

Think of Cocoon as a guard dog (dogs are known for their ability to hear ultrasound, or sound frequencies above 20,000 Hz, while infrasound is below 20 Hz but you get the idea); one that can send you a push notification and an email whenever something seems amiss. And of course, it can also detect run-of-the-mill sound frequencies too.<