You can also send Sentry's alerts into Pagerless: Sentry to Pagerless. Compare: Pagerless vs Sentry alerts.
Questions
Do I need Sentry or an on-call tool like PagerDuty?
They do different jobs. Sentry tracks and helps debug errors; its free plan alerts by email only and it doesn't call your phone. On-call tools decide who to wake and reach them by push and phone. Many teams use both; Pagerless adds diagnosis and one-tap undo to the on-call side.