A dusty old one from the back of the store cupboard: a Maxon SMX-4O50NLA!
We haven’t really used these since 2012 (yeah, that late!), but we do have one still fitted out in a car so we can contact the guy should we need to (cos phones, yeah).
There are loads of these that look that same, but I can identify this one from the serial number and details on the back (there are another 20, most of which have the details scuffed off):
I believe that these can be programmed to 4, but it isn’t that easy.
This is another one that belongs to my employer, so I can’t fuck about with it yet.