Don't need GPS - WIFI connection can cover home and work. I personally don't suggest any automation for car mode. It should be manually started / stopped for safety sake unless you have an accurately-made car dock.
... and I could help by suggesting that you shouldn't use GPS for trying to figure out home/work/car, but rather a combination of WiFi and accelerometer data. Using GPS often will drain a battery faster than your users will uninstall the app.