Just be careful using those as a speedometer on the highway, gps on certain devices is allowed to be out by a certain % and some a lot more then others, and even some apps show different..it's not a whole bunch, but if you were on the highway and already possibly pushing things, it could be out a few mph and have you over what that cop deems ok that day. There are actual speedometer gauges you can buy and mount permanent that look like classic gauges that use a gps unit mounted in the truck and no subscription needed, and no worries about forgetting phones or dead cell batteries..but they are a bit pricier then most gauge sets, and are only 12volt I believe.