iphone small app

I'm looking for an iphone programmer that could help me create a script to calculate small changes in altitude in the iphone. I would also like to run this script in the background of the iphone and keep it always on. I do not need the script to work at less than 10Hz per sec. In fact, if it saves battery, I'm fine checking once every 10 or 30 seconds. If the script detects changes in altitude it will trigger a message on the iphone screen asking the user to confirm the change. A simple message such as Did the Altitude Change? and ask the user to respond by a yes or no. THat's it. I saw an already made script on Google. I could share the URL if you need it. I need the app to work for at least 8-10 hours without draining the battrery. I believe one way of allowing the app to run continuosly even when the phone is locked is to use the GPS feature. However, unless used in a limited way (not connected to the satellite) it might drain the battery in a less than a couple of hours. Also, I'm not 100% sure the GPS is needed for this app. The accelerometers will probably do the trick pretty well if we're able to get them to function all the time (even with locked phone)