Most stations broadcast on a special VHF frequency band at 162MHz, which has seven narrowband FM channels. The original frequency was 162.550, with 162.400 and 162.475 being added later. In recent years, the proliferation of stations meant to make sure everyone has access to warnings has pushed that number to seven, now including the "intermediate" channels of 162.425, 162.450, 162.500, and 162.525MHz. These channels (often numbered in that order) are available on special weatheradio receivers, available across both countries by mail-order and at some retailers such as Radio Shack. Some stations in Canada also broadcast on regular FM and AM broadcast stations.
When a weather warning is issued for the area which a station covers, certain weatheradios are designed to turn on or sound an alarm upon detection of a 1050Hz tone, issued for ten seconds immediately before the warning message. In the U.S., newer radios can instead detect a digital-over-audio protocol called Specific Area Message Encoding or SAME, which allows the radio to limit alarms to only certain warnings, and only to the actual section of the broadcast area which the listener is located. (This system later became the Emergency Alert System now required by the FCC for broadcast stations.) In Canada, many stations operate Weathercopy, which is a higher-speed version that can actually transmit entire text forecasts and warnings, but is not designed for alerting.
The bulk of programming however is still in regular voice rather than digital, with a forecaster recording each message once and a system having it repeat in a loop. In the U.S., the NWS has now installed a console replacement system (CRS). which uses a synthesized voice to read text announcements. The voices have recently been upgraded with new software that gives a much more realistic and pleasant male or female voice, and also allows intonation so that the tone of voice changes with the urgency of the message being read. Many stations also broadcast in other local languages, including both french and english in Ottawa/Gatineau, Montréal, and the city of Québec; french-only in other parts of Québec province, and synthesized in both english and spanish in Puerto Rico.