A first alarm of a plurality of alarms that form a multihop network extending from a relay device, comprising: a communication unit capable of communicating with the relay device with a hop count i (i is an integer equal to or larger than 1) and also capable of communicating with a second alarm and a third alarm capable of communicating with the relay device with a hop count i+1; a first communication time slot in which the first alarm is configured to transmit a communication signal, a second communication time slot in which the second alarm is configured to transmit a communication signal, and a third communication time slot in which the third alarm is configured to transmit a communication signal being arranged on a time axis, a first monitoring time slot in which the first alarm is configured to transmit a monitoring signal and a second monitoring time slot in which the second alarm or the third alarm is configured to transmit a monitoring signal being arranged earlier than the first communication time slot, the second communication time slot, and the third communication time slot, and the first monitoring time slot being arranged later than the second monitoring time slot, the first communication time slot being arranged later than the second communication time slot and the third communication time slot, the alarm further comprising: a monitoring unit configured to monitor reception of the monitoring signal in the second monitoring time slot; a control unit configured to suspend a process of receiving the communication signal in the second communication time slot and the third communication time slot when the monitoring unit does not detect reception of the monitoring signal, and the control unit being further configured, when the monitoring unit detects reception of the monitoring signal, to cause the monitoring signal to be transmitted in the first monitoring time slot and then cause the communication signal to be received in the second communication time slot or the third communication time slot and then also cause the communication signal which was received in the second communication time slot or the third communication time slot to be transferred in the first communication time slot. a communication unit capable of communicating with the relay device with a hop count i (i is an integer equal to or larger than 1) and also capable of communicating with a second alarm and a third alarm capable of communicating with the relay device with a hop count i+1; a first communication time slot in which the first alarm is configured to transmit a communication signal, a second communication time slot in which the second alarm is configured to transmit a communication signal, and a third communication time slot in which the third alarm is configured to transmit a communication signal being arranged on a time axis, a first monitoring time slot in which the first alarm is configured to transmit a monitoring signal and a second monitoring time slot in which the second alarm or the third alarm is configured to transmit a monitoring signal being arranged earlier than the first communication time slot, the second communication time slot, and the third communication time slot, and the first monitoring time slot being arranged later than the second monitoring time slot, the first communication time slot being arranged later than the second communication time slot and the third communication time slot, the alarm further comprising: a monitoring unit configured to monitor reception of the monitoring signal in the second monitoring time slot; a control unit configured to suspend a process of receiving the communication signal in the second communication time slot and the third communication time slot when the monitoring unit does not detect reception of the monitoring signal, and the control unit being further configured, when the monitoring unit detects reception of the monitoring signal, to cause the monitoring signal to be transmitted in the first monitoring time slot and then cause the communication signal to be received in the second communication time slot or the third communication time slot and then also cause the communication signal which was received in the second communication time slot or the third communication time slot to be transferred in the first communication time slot. a monitoring unit configured to monitor reception of the monitoring signal in the second monitoring time slot; a control unit configured to suspend a process of receiving the communication signal in the second communication time slot and the third communication time slot when the monitoring unit does not detect reception of the monitoring signal, and the control unit being further configured, when the monitoring unit detects reception of the monitoring signal, to cause the monitoring signal to be transmitted in the first monitoring time slot and then cause the communication signal to be received in the second communication time slot or the third communication time slot and then also cause the communication signal which was received in the second communication time slot or the third communication time slot to be transferred in the first communication time slot.