The user monitor module 20 is a portable device that may include a transmitter capable of emitting one or more kinds of {TAIL ~ signals} and {HEAD ~ a receiver} capable of receiving an external signal 
The user monitor module 20 is a portable device that may include a transmitter capable of emitting one or more kinds of { TAIL ~ signals } and { HEAD ~ a receiver } capable of receiving an external signal
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH