In the United States, the standards in the 2009 MUTCD require APS units to have a pushbutton locator tone, audible and vibrotactile walk indications, a tactile arrow aligned with the direction of travel on the crosswalk, and to respond to ambient sound. The pushbutton locator tone is a beep or tick, repeating at once per second, to allow people who are blind to find the device. If APS units are installed in more than one crossing direction (e.g. if there are APS units at a curb for both the north–south and west–east crossing directions), different sounds or speech messages may be used for each direction. Under the MUTCD guideline, the walk indication may be a speech message if two or more units on the same curb are separated by less than . These speech messages usually follow the pattern "name. Walk sign is on to cross Name." Otherwise, the walk indication may be a "percussive tone," which usually consists of repeated, rapid sounds that can be clearly heard from the opposite curb and can oscillate between high and low volumes. In both cases, when the "don't walk" indication is flashing, the device will beep at every second until the "don't walk" indication becomes steady and the pedestrian countdown indication reaches "0", at which point the device will beep intermittently at lower volume. When activated, the APS units are mandated to be accompanied by a vibrating arrow on the APS during the walk signal.