If I am on call 24/7 how do I convey this to a potential second employer? [CA]

Apologies if this is the wrong flair. I just thought this would be the right one.

Basically im on call 24/7 and I get paid for just carrying the pager around for when I do get after hours calls and emergencies as a security supervisor.

I do not make enough money and want to get a second job that will supplement my income. There has been no emergencies as of yet and little to no after hour calls (past 3pm when I am off site). But this is something I need to do in order to "survive" paying down my debts.

How do I convey something like this to a new employer when they ask for full time availability?

Some days after hours if say for example an alarm is going off at my main job, I would need to take care of this either in person or over the phone with someone there already. Or possibly I will get an emergency call of a gate not operating and crushed a car or something. These are the types of emergencies I could get a call about and being a security supervisor I would have to attend to this right away