NOAA Weather Radio broadcasts on the following frequencies across the country. These are the ONLY frequencies specifically designated for this purpose and are re-used in areas that aren't close enough to interfere with each other (example - 2 stations using 162.400 are far enough apart that they can't both typically be heard at the same time):
162.400 MHz
162.425 MHz
162.450 MHz
162.475 MHz
162.500 MHz
162.525 MHz
162.550 MHz
Each location is designated to cover a specific area (even though the signal may be easily heard in other "regions" as they are also set up to overlap somewhat) and all alerts for that area will be sent out on that frequency. The ongoing loop it broadcasts is general weather information and repeated alerts/warnings that may be active. There is no frequency ONLY for alerts. All S.A.M.E. weather alert radios monitor these frequencies... you pick the one that covers your specific area... but can be set to only turn on or "activate" when an alert that affects that area is sent out. Two-Way radios (ham, GMRS, MURS, etc) that are capable of receiving these frequencies may or may not also have an "alert" feature where you would only hear the audio if an alert was issued but again... that would be the only way to not hear the "looped" or repeated information.