Walky Talkies
a great selection of walky talkies
Popularised in those ancient American WWII films, walky talkies are actually quite practical devices and are no means obsolete in the mobile phone era. If you need to communicate with staff around a warehouse or a site then they're way better than a mobile.
Using mobile phones to communicate is precarious at the best of times. In any kind of situation where you need to be able to communicate quickly, just thing what that means with a mobile. First you have to dig the thing out of a pocket, possibly with a cold gloved hand, and then deal with complicated menus and fiddly little buttons. Once that's done you have to hope you have a decent signal and the person on the other end isn't ringing somebody else.
Well that's not much of a problem in a nice warm urban situation, but security guards patrolling a site late at night or groups exercising on open moorland might view it from a rather different perspective. In a situation like that, walkie talkies with a 5km range are far more suitable, less likely to get nicked, and a whole lot cheaper to run.
In fact if I were organising any kind of event in wild country, like a moortop fund raising walk or the forest stages of a rally, I wouldn't consider using anything else. When I was recently shooting at the NRA ranges at Bisley, and I noticed all the range staff there are equipped with them. Now that's common sense as any kind of alert can be broadcast to all the rang staff with immediate effect.