G PHYSICS
G08 SIGNALLING
G08B SIGNALLING OR CALLING SYSTEMS; ORDER TELEGRAPHS; ALARM SYSTEMS
21/00 Alarms responsive to a single specified undesired or abnormal condition and not otherwise provided for
G08B21/02 Alarms for ensuring the safety of persons
G08B21/0202 Child monitoring systems using a transmitter-receiver system carried by the parent and the child
G08B21/0225 Monitoring making use of different thresholds, e.g. for different alarm levels