What is a dial tone?

A dial tone is a continuous buzzing or hum sound heard on a telephone line when the receiver is lifted and before a call is made. It indicates that the line is active and ready for dialing. In traditional landline telephones, the dial tone is generated by the telephone company's central office equipment. When the dial tone is absent or sounds different than usual, it can indicate a problem with the telephone line or equipment. In modern digital telephone systems, the dial tone may be simulated electronically rather than generated acoustically.