BabyGuard lets you know by phone when your baby wakes up.The app can run on your old iPhone after you have upgraded to a newer model. We recommend using Free Family Calls or a smartphone family discount.BabyGuard calls to a registered phone number are triggered by any major tilt or positional change for the old iPhone, based on the accelerometer's ability to pinpoint its location in three dimensions.You can hear if your baby is crying, and respond with a parent's soothing voice. Put your old iPhone in the baby's cot, and push the START button on the BabyGuard touch screen.This activates the accelerometer, which disregards data from the first 20 readings, and generates an average from the next 20 readings to define its 3D base location. Monitoring is then initiated, and it is stopped and re-initiated at one-minute intervals thereafter. Setting the screen to a low brightness conserves the battery.When active, the monitoring screen displays location on three-dimensional axes (X, Y, and Z). Some older iPhones always display the location as 0.000000. In that case, please use another iPhone.When your baby wakes and stretches, the iPhone moves, the accelerometer detects the altered location, and you can be sure of getting the news with a call from BabyGuard.