How do you explain on-call weeks to a 4 year old?

One week in four I'm on call for our database systems. My laptop comes everywhere, and twice this month it went off in the middle of bath time and I handed her to my partner mid-shampoo. She now asks every morning, 'Are you on call today?' and if I say yes, 'Will you go away in the middle?' She isn't upset exactly. She's planning. So far I've said 'Mama has a work phone that rings sometimes.' Is there a better way to put it at this age, so she knows what to expect without it becoming something she worries about? ❤️