According to an aspect, there is provided switch circuitry (1) for controlling power supplied to a fluid monitoring unit (4). The switch circuitry (1) comprises: a sensor (2) configured to detect fluid derived from the skin of a user and to generate a detection signal in response to detection of fluid； and a controller (3) configured to receive the detection signal, to generate a wake-up signal in accordance with the detection signal, and to supply the wake-up signal to a switch (6) controlling the power supply to the fluid monitoring unit (4) so as to activate the switch (6) and wake the fluid monitoring unit (4), wherein, optionally, the fluid is sweat. According to another aspect, there is provided method of controlling power to a fluid monitoring unit.
