In order to ensure that the tracker works in the best possible way, it is best to check the Helium coverage in your target area of usage before you buy a tracker.
You can do this by visiting the Helium website or the beta page, which will show you the various active hotspots.
Please note that the network is still rolling out, and new hotspots are added each day globally, so coverage will improve with time. Why not buy a hotspot for your home?