You will need a P25 (digital) scanner for sure. Your best bet is to listen to the (2) Charleston County 800MHz systems. There is an analog Motorola SmartNet 800MHz trunked system and the P25 digital system as well. Kiawah Island security is on UHF.
EMS and CC Sheriff's Office are on the P25 system. I think that the St. Johns FD which covers Johns, Kiawah, Wadmalaw, and Seabrook Islands is still on the analog system.
No matter what, make sure that you check the database.