An embodiment of the invention is a modular card style radio-signal modem suitable for wireless data communication to a personal computer. The ultrasound probe is configured to interface with an axial end of the fastener, to emit ultrasound signals into the axial end of the fastener, and to receive ultrasound signals from the fastener. The rotating head facilitates a smooth engagement between the trimmer head and the obstacle as the trimmer head moves around the obstacle.