A presence alert system (24) includes a sniffer (36), controller-circuitry (38), radio frequency (RF) background data (40), and a software program (42). The sniffer is configured to sample and measure a characteristic of ambient RF signals (33) over time. The controller-circuitry includes one or more processors and one or more storage mediums. The RF background data is stored in at least one of the one or more storage mediums, and is indicative of no moving presence. The software program is stored in at least one of the one or more storage mediums, and is executed by at least one of the one or more processors. The software program is configured to evaluate the measured characteristic of the ambient RF signals, compare the measured characteristic to the RF background data, and thereby determine motion of a presence (34).