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 a receiver capable of receiving {HEAD ~ 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 a receiver capable of receiving { HEAD ~ 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 OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD