One Receiver can match several transmitter.So if you have two kids,you only should buy 1 Receiver and 1 extra transmitter.

Child Guard Wristband Anti-Drowning Alarm                                                                       1) The unit consists of an alarm Receiver and a Transmitter which can be locked onto the child's wrist;                                                                                                                    2) The Receiver will sound an ALARM and a Warning Light also FLASHES  when the transmitter immerse water;                                                                                               3) Alarm voice level is approximately 100 decibels;                                                             4) Maximum range from Tansmitter to Receiver is 200 feet (60 metres approx);                                                                                                                          5) Wristband works on CR2032 battery, battery life is 3 years;                                            6) Receiver works on AC adapter OR Rechargeble 9v battery;                                              7) Rechargeable battery can last 6 hours when it's fully charged;                                         8) Base unit has a Low Battery Alarm when the rechargeable battery is nearly using out;                                                                                                                                      9) Reset and Test button                                                                                          

Pool Alarm&Pool Scout