GPS tracking application for iphone and android

The problem: - I have workers that claim they are on site working and they are actually at their hotel sleeping. I need an application that runs on the phone and keeps a log of their whereabouts every 15 minutes. This can be through a simple log of gps coordiantes every 15 minutes that can then be translated to google map location and timeline.
I am pretty open to options an ideas, but would like a complete solution that will work in both android and Iphone.