An activity monitoring system comprising a plurality of wireless units wherein a first wireless unit comprises a wireless transceiver to broadcast at least one timing signal; a second wireless unit comprises: a wireless transceiver to receive at least one signal; a monitoring device that generates monitoring data; a memory to store the monitoring data; a processor to synchronize a time with the corresponding monitoring data; and wherein the second wireless unit: processes the received timing signal from the first wireless unit; synchronizes the monitoring data with the timing signal resulting in a time-synchronized data stream.