My car was left unlocked in my basement garage (locked and not public) and my navigation device was left in the car.

As you can imagine, the device was stolen.

Before I call my insurance company about this, does the fact that the car was unlocked mean it was pure neglegence on my part, making any attempt at an insurance claim futile?

The thieves even had the courtesy to put the cigarette lighter back into the socket after stealing the TomTom charger. The lighter was in the glove compartment.