i picked up a few of the
garmin 530 hcx... these are frs/gmrs two way radio communication devices with built in gps (having only one would be pointless). when you have a dialogue between two or more of these units they basically show up on your map so autolocation is the key purpose. it has a waterproof rating that's pretty low but better than most (it can get wet, just not to deep or wavy). great compass and trip computer, you'll not only know speed, direction, duration of movement and stops, virtical drop and rate of said drop, and way tmi. your radio has multi band communications (technically you should be licensed to use gmrs btw) and multiband weather.
now the best part is the gps with it's map displays.
topo is your terrain info,
city navigator gives you street and turn by turn directions,
bluechart provides soundings and bathymetric charts of underwater features such as reefs and shouls... and there's more. the maps come at a price though and with this product it can get expensive. but like everything else, nothing is safe from a cleaver hack.
so what's the purpose of all this... using your topo you find the steepest roads in the area and check it against citynav for intersections and such... set your spotters who can contact you even if it is a long winding hill and you do not have a visual. take your run and record your track data (ie: speed, direction, gradient, etc) using the trip computer. along comes the man and you have to split... using the radios you know the exact location of the others especially if you have to disperse. another purpose is for finding the surf... weather radio lets you know the small craft advisories, bluechart gives you the underwater terrain to find the features that would offer potential for wave formation given the right weather pattern. using the radio you can do your soundings to catalogue these potential surf spots. get the picture?