AT commands AT is a contraction of attention, a command used to program SmartModems from Hayes Microcomputer Products. AT commands program a variety of modem hardware settings and were adopted by other modem manufacturers who wanted to market their wares with the coveted phrase Hayes-compatible. At one time, you couldn't call yourself an online aficionado if you didn't know that ATL0 turned your modem speaker way down and ATM0 turned it off. Now the commands are usually hidden under a menu option in your communication software. See also: Hayes-compatible