Android: Get value from background service?

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http://stackoverflow.com – I made an app where user picks location and clicks start, then it opens a new activity and shows current location and ETA to destination, simultaneously background service is also started - a GPS service, it keeps reading current location and calculating ETA. Now my problem is: How would I provide ETA screen with data, I have two options I see: 1) Run another GPS action at same time calculating distance to destination but I suspect that will drain battery in no time. 2) Get data from already running GPS service in background? How would I go with option two? By the way, service is needed so (HowTos)