Geofencing let me draw a simple circle on a map, using either the Delphi Web site or the app, and Vehicle Diagnostics sent an alert whenever the car was driven outside of that range. This feature reveals the biggest use for the Vehicle Diagnostics module: keeping track of the kids.
Using the Web site, drawing the geofence was easy, but on the app it was much more difficult. That makes using the feature on the fly, such as when you've handed your keys over to a valet, impractical.
Vehicle Diagnostics also includes the option to track your car live on a map, but this feature needs to be activated on an individual basis. Such a feature is data-intensive, so I imagine Verizon doesn't want it active at all times.
The app also shows the car's current fuel level, whether the engine is running, and the battery status. This last bit of information can be useful if you've left your car at an airport and need to know if you will need a jump-start when you get back to it.
Missing is any fuel consumption information. It would be useful if the Vehicle Diagnostic system included a trip computer so you could remotely monitor your gasoline usage, or check to see if the car was consuming more than it should.
The app also includes a virtual key fob feature, which you can use to lock or unlock the doors, start the engine, and honk the horn. However, it wasn't compatible with the Mini Cooper I used for testing. Delphi's car compatibility tool does a good job of showing what features work on different models.
Another limitation I found was that, for many of the features to work, the car has to be within Verizon's coverage area. That signal could not reach into CNET's basement garage, so I ended up with incomplete data when I parked the car at the office.
Cost is another negative factor. The Vehicle Diagnostics module itself only costs $249, but you will also need a Verizon data plan, which comes in at $35 per month. Current Verizon customers can add the Vehicle Diagnostics system to an existing data plan.
Single drivers likely won't find the Vehicle Diagnostics feature set compelling enough to fork over the cash, although there is some novelty in getting this data on your phone. Parents, however, will find it a worthwhile means of keeping tabs on their driving-age children.
Technically apt kids might discover the device's location and remove it for trips outside of their parents' prescribed geofence, but the slightly complicated setup procedure works in the device's favor. If a kid can't figure out how to get it running again properly, the parent will know something's up.