This project is building a wireless sensor network for a room-scale Theremin instrument using ZigBee protocol. The Theremin is an instrument that is played entirely without touching it. The instrument based on electromagnetic fields, which are being "disturbed" by the limbs of the player. Theremin has two antennas, vertical antenna for controlling the pitch and horizontal antenna to control the volume. Unfortunately, the playing of Theremin is limited to the area around the antenna. This case, however, also means that it will be necessary to redesign the theremin in some aspects. We will try out a couple of ultrasound sensors, which will be used to detect the movements of the player’s bodies. We also utilised those ultrasound sensors along with microcontroller, FreeRTOS, and ZigBee devices to create a wireless sensor network. In the end, after did some evaluations and concluded that to replace the electromagnetic field, we can use the ultrasound sensors. Besides, ultrasound sensors have a decent accuracy to measure an object distance. Our room-scale Theremin (we call it Thereminz) make music using MIDI by converting the detected distance into MIDI note. We configured Thereminz to create MIDI note-on, note-off, and pitch bend to particular movements.