The best thing about the Mom-Kid Cares wireless child tracker is its cheap price ($US9.90) and its Hong Kong English descriptive text:

Mom-Kid Cares Operation :
# The transmitter can hook to the object (a Kid), and place the receiver in the pocket.
# When the object (a Kid) is lost or stolen outside 4 ~ 5.5 meters, the receiver will alert.

Mom-Kid Cares Description :
# Easily and Widely use in different area, such as, Mobile, Wallet, Kids, Keys, etc. It's for security and protection purpose.
# Two range setting, Short: 4 meters, Long: 5.5 meters.

Mom-Kid Cares, $US9.90 [brando.com.hk via dt reader Ed. (not the ed. who makes all the meta-comments, though, just so you know)]