Embedded system with SMA connectors
For GPS receivers in particular, many of them use an "active" antenna that has a built-in preamp, and requires typically 3.3V or 5.0V at a few 10s of mA of DC power fed down the coax. Some GPS receiver modules actually monitor the amount of current being drawn by the antenna and can alert you if it is either too low (cable open) or too high (cable shorted).

Other GPS modules don't monitor the current themselves, but they do have a separate power input specifically for antenna power, to which you can add your own monitor circuit.

Unfortunately, WiFi antennas are usually passive, so the same technique can't be used there.