What is meant by "being on call"?

The Chappaqua Ambulance is staffed year round, 24 hours a day, by volunteers. "On call" means you are responsible to respond to a request for ambulance service. You will be alerted by a pager that is provided. You may respond from home, or wait at the ambulance building, Starbucks, library or anywhere in Chappaqua that is within 5 minutes of our building. We provide a green rotating light for your car that will help you navigate traffic to get to CVAC Headquarters and join the ambulance crew.