There are several features to for in a NOAA Weather Radio. The most desirable feature is an alarm tone. This allows you to have the radio turned on but quiet, listening for a special tone that is broadcast before watch and warning messages. During an emergency, National Weather Service Forecasters will interrupt routine weather radio programming and send out a special tone that activates the NOAA Weather Radios in the listening area.
A new generation of NWR receiver allows you to pre-select the National Weather Service alerts you want to receive according to local geographic areas (counties or in some cases portions of counties). Look for NWR receivers with the SAME feature (Specific Area Message Encoding) which means that the receiver is capable of turning itself on from a silent mode when the digital code is broadcast before the alarm tone is sounded for the geographic area which you have pre-selected.
In addition, a good receiver should be able to operate on batteries during times when electrical services may be interrupted. Look for radios with an AC adapter and battery compartment. The radio should be tunable or switchable to all seven NWR frequencies. Some older models receiver only three frequencies which will not work in all locations.