A wireless power transfer device may include a circuit couplable with a coil to transmit or receive a first signal providing wireless power through the coil. The first signal may be modulated with second signals. A packet within any of the second signals may include first bits associated with a preamble and second bits associated with data. The device may further include a controller to measure temporal variations of at least one of the first signal, a rectified version of the first signal, or the one or more second signals. The controller may further determine thresholds for distinguishing between bits in the packet based on the temporal variations. The device may further demodulate the signals using the one or more thresholds to identify the preamble of the packet and extract the second bits associated with data from the packet when the preamble of the packet is identified.