I do not know what it is but my immediate thought was some kind of security tracker; in the UK it isn't uncommon for insurance companies to ask for them to be fitted to vehicles which have a value above a certain level. However, these are normally hidden quite well and thus I doubt this would be the control unit for such a system. However, if you have any paperwork for a tracking device, in the history file, this could be worth looking into. On a side note, I purchased an old car, which had such a device fitted but was no longer in use. Over time I noticed a battery drain and managed to trace it back to the defunct tracker. Although the previous owner had chosen to not renew the annual subscription, the device was still installed and drawing constantly from the battery of the car; not an issue when the car was in use but quickly depleted the battery when it was not!
