Hywel Dda University Health Board is the first in Wales to launch the "Push the Button" system to curb smoking at Carmarthenshire, Ceredigion and Pembrokeshire hospitals.
It enables people to anonymously push a red button which triggers an announcement reminding them hospitals are smoke-free.
The policy also includes e-cigarettes.
The bilingual messages were recorded by pupils at Pembrokeshire's Wolfscastle school and the buttons can be found near the main entrances to Bronglais, Glangwili, Prince Philip and Withybush hospitals.
Teresa Owen from the health board said: "While the majority of staff, patients and visitors to our sites respect this policy, some people continue to smoke on-site.
"Everyone has the right to breathe fresh air, especially when visiting a health care facility and we regularly receive complaints about people smoking on our sites."
A PA system is being launched at hospitals in mid and west Wales to discourage smokers from lighting up.