Emergency Response:

Immunity from liability for emergency care–Exception. No peace officer, conservation officer, member of any fire department, police department and their first aid, rescue or emergency squad, or any citizen acting as such as a volunteer, or any other person is liable for any civil damages as a result of their acts of commission or omission arising out of and in the course of their rendering in good faith, any emergency care and services during an emergency which is in their judgment indicated and necessary at the time. Such relief from liability for civil damages extends to the operation of any motor vehicle in connection with any such care or services.

Nothing in this section grants any relief to any person causing any damage by his willful, wanton or reckless act of commission or omission.

Automatic External Defibrillator:

Civil immunity for emergency use or nonuse of AED. Any person, who in good faith obtains, uses, attempts to use, or chooses not to use an AED in providing emergency care or treatment, is immune from civil liability for any injury as a result of such emergency care or treatment or as a result of an act or failure to act in providing or arranging such medical treatment.

http://sdlegislature.gov/Statutes/Codified_Laws/DisplayStatute.aspx?Type=Statute&Statute=20-9-4.1
http://sdlegislature.gov/Statutes/Codified_Laws/DisplayStatute.aspx?Statute=20-9-4.4