在电话技术中，利用音调在电路中传送监控、地址和报警信号的做法。 In telephony, the use of tones to transmit supervisory, address and alerting signals over a circuit.
在电话技术中，电话操作员使用的一种信号，用来获得另一次注意，或由操作员保持的用户发送的一种信号，用以获得随后的注意。 In telephony, a signal used by a telephone operator to gain the attention of another, or a signal sent by a subscriber held by an operator to gain the latter's attention.
