WAY (Warning Area Alerts) tells you when other devices enter or leave a specified location.

If you need help tracking other Android devices from your phone, WAY is a solution you should consider. WAY will track the locations of the phones of the people in your immediate circle (spouse, parent, child) and notify you when they enter a location grid that you've previously specified. This can be useful for a number of reasons: planning a surprise party, cleaning the house before your spouse gets home, and checking that your child got home safely are just a few of the usecases for WAY.