This disclosure relates to using a wake up signal in conjunction with cellular communication in unlicensed spectrum. A cellular base station may provide a wake up signal on an unlicensed frequency channel after successful completion of a listen-before-talk procedure. The wake up signal may include a preamble configured for coherent detection, and information indicating channel occupancy time for a cellular communication by the cellular base station and a cell identifier for the cellular base station. A wireless device may monitor the unlicensed frequency channel for a wake up signal, and may determine whether to monitor the unlicensed frequency channel for control channel signaling based on whether a wake up signal is received, and potentially also based on the contents of the wake up signal if a wake up signal is received.