trust me we had them and they will no if you mess with it the ones we had were NAVMAN it told them when the van was running when you had turnd the key to put the radio on how fast you was going were you was wot time you set of wot time you got there wot miles you did to get to work so they new wot to take out of you pay they worked awer pay from it .....the one night the battery was flate so i put a new one on i got into work the next day and my doss at the time went mad at me saying i was trying to mess with it when i put the bill in his hand he shut up and i nerver got a sorry for wot he said to me .............THAT WAS MY OLD JOB ..........GOT A NEW ONE NOW LOT BETTER NO FUCKING TRACKERS