Worktime Keeper uses GPS technology to count spent time in the work. When you go for lunch and move away, geo location stops counting time. When you come back to work, it continues counting.
If time is near of the end of work, app notifies you.
Continued use of GPS running in the background can dramatically decrease of battery life. So when you are in the work, plug your iPhone on USB cable.
Time in this app is for you own information and it is not for exact time measure.