My phone reminder didn't go off

You set it. The time came and went. Nothing happened — no sound, no banner, nothing on the lock screen when you checked afterwards. This page is about that specific failure: the alert never arrived at all.

Start by working out which failure you actually had, because the fixes are completely different:

It fired, but you couldn’t hear it. There was a notification waiting when you looked. That’s a sound problem, and the fixes are in reminders that work when your phone is on silent.
It fired, you saw it, and it’s gone. You swiped it away half-consciously and have no memory of doing it. That’s a reminder you can’t swipe away.
It fired, but at the wrong time. An hour early, an hour late, or hours out after a trip. That’s a clock problem rather than a delivery problem — there’s a section on it below, and the causes are completely different from everything in the list that follows.
It genuinely never appeared. Nothing in Notification Center, nothing in history. Keep reading — that’s this page.

Almost every cause below is a phone setting, it’s free to fix, and it takes under a minute. Work down the list in order; they’re ranked by how often each one is the actual culprit.

iPhone: the six things that silently kill a reminder

1. Notification permission got switched off — often by an update. This is the most common cause and the least obvious, because nothing tells you it happened. Go to Settings → Notifications → the app, and check Allow Notifications is on. A major iOS update, a restore from backup, or reinstalling the app can reset this, and the app carries on looking like it’s working — reminders save fine, they just have nowhere to be delivered. If you’ve had a run of missed reminders that started around an update, this is almost certainly it.

2. A Focus mode swallowed it. Settings → Focus. Check whether a mode was active at the reminder time — Sleep, Work, Driving, or a Personal focus you set up once and forgot. Focus modes are scheduled, so one can be running without you turning anything on today. Add the app under Allowed Notifications, or mark the app’s alerts Time Sensitive (Settings → Notifications → the app), which lets them break through a Focus by design.

3. Scheduled Summary held it until later. Settings → Notifications → Scheduled Summary. If the app is in the summary list, its reminders don’t arrive when they fire — they’re bundled and delivered at 8am and 6pm. A reminder for 2:15pm silently becomes an item in a digest at six o’clock. Take the app out of the summary; the whole point of a reminder is that it’s punctual.

4. Ringer volume and alarm volume are separate. Worth checking even though it sounds like a sound problem, because it produces an alert you never perceive at all: turning your ringer to zero with the side buttons doesn’t touch alarm volume, and vice versa. Settings → Sounds & Haptics → check the Ringer and Alerts slider, and whether Change with Buttons is on.

5. The reminder wasn’t set for when you think. Check the entry itself. AM/PM slips are ordinary, and if you set it while travelling or after a flight, a time-zone-anchored reminder can be sitting hours away. Also check it isn’t scheduled for a date already past — an overdue reminder just sits there quietly.

6. Low Power Mode and background delivery. Low Power Mode reduces background activity, which can delay app-generated alerts that rely on the app doing work. It won’t stop a properly scheduled local notification, but it’s a real contributor if your reminders arrive late rather than never.

Android: two extra causes that don’t exist on iPhone

If you’re on Android, check the iPhone list’s equivalents first (notification permission, Do Not Disturb, volume) — then these two, which cause most Android-specific misses:

Battery optimisation is killing the app in the background. Settings → Apps → the app → Battery → set it to Unrestricted. Aggressive power management — especially on Samsung, Xiaomi, OnePlus and Huawei devices — will suspend a backgrounded app entirely, and a suspended app cannot fire anything. Some manufacturers also have a separate “protected apps” or “auto-launch” list the app must be added to. This is the single biggest cause of vanished Android reminders.

Android 12 and later need explicit alarm permission. Settings → Apps → the app → Alarms & reminders must be allowed. Without it, exact-time scheduling silently fails or slips to whenever the system feels like it. It’s a permission most people have never seen a prompt for.

It fired, but at the wrong time

This is the sibling failure, and it’s worth separating because none of the fixes above touch it. The reminder did arrive — just not when you meant. Three causes account for almost all of it.

Daylight saving, and it lasts for weeks. This is the big one, and it’s badly understood. When the clocks change, reminders that were stored against a fixed instant rather than a wall-clock time start arriving an hour early or an hour late — and they keep doing it until something re-anchors them. If your reminders drifted by exactly an hour and the date lines up with a clock change, you’ve found it. Delete and re-create the affected reminders rather than editing them; a fresh entry re-anchors cleanly.

You changed time zones. After a flight, an app can be holding your reminder against the zone you set it in, the zone you’re now in, or your calendar’s home zone — and different apps make different choices. A 7am reminder set in London can land at 2am in New York, or not until the afternoon. The tell is that everything is out by the same offset, and that offset matches your travel.

Sync lag between devices. If reminders live in iCloud or a Google account and you edit them on one device, another device can act on a stale copy for a while — firing an old time, or firing a reminder you already deleted. Open the app on the device that’s misbehaving and let it sit connected for a minute before you conclude it’s broken.

For what it’s worth on our side: ReminderCall stores each reminder against a named IANA time zone and resolves the daylight-saving offset at the moment the call is due, server-side, so a clock change doesn’t shift an existing reminder. The honest limit is the other half of that — it uses your device’s time zone and there’s no picker to override it, so if you set a reminder for someone in another zone, or you want a time pinned to home while you travel, you need to do that arithmetic yourself. There’s more on that in remembering to call family in a different time zone.

Why this keeps happening

If you fixed one of the above, you’re done — genuinely, go and set your reminder again and stop reading.

But if it’s happened repeatedly across different apps, it’s worth understanding the structural reason: a notification has a long chain of things that must all work. The app has to be alive or correctly scheduled, the OS notification stack has to accept the alert, no Focus or summary rule can intercept it, and a push-based reminder additionally needs a working data connection at that exact moment. Every link is invisible, and when one breaks, the failure is silent — nothing tells you a reminder didn’t arrive. You find out from the consequence.

That’s also why swapping one reminder app for another so often changes nothing. Every app on your phone is delivering through the same stack, subject to the same settings.

A call is a different delivery path

This is the one place ReminderCall is relevant, and it’s a narrow claim: a phone call doesn’t travel through the notification system at all. It arrives over the cellular voice network, needs only a bar of signal rather than a data connection, and follows your ring settings instead of your notification settings. The layer that just failed you isn’t involved.

Precisely what happens: at the time you set, it places one real phone call to your number and a voice reads your own words aloud — “blood pressure tablet, and the car’s booked in at four.” It rings for roughly twenty seconds — four or five rings — deliberately ending before voicemail can intercept it. If you don’t answer, the reminder arrives as a text message instead, so it’s on your lock screen when you next look. It does not redial you, and it doesn’t notify anyone else. There’s more detail on how that differs from a notification.

And the one setup step that decides whether any of that works. iOS has a setting called Silence Unknown Callers (Settings → Apps → Phone). With it on, a call from a number that isn’t in your Contacts, isn’t one you’ve recently dialled and isn’t a Siri suggestion goes straight to voicemail with no ring at all — the same silent, invisible failure this whole page is about, just on the call path instead of the notification path. A reminder call counts as unknown until you save the number as a contact, which is why the app asks you to do that during setup. If you’ve switched to call reminders and a call has simply never arrived, check this before assuming the service failed. Saving the number is also what Emergency Bypass attaches to, so the one step buys you both.

Honest caveats

A call needs carrier signal like any other call. No signal at reminder time, no call — the SMS backup lands when coverage returns.
ReminderCall is a reminder service, not a medical or emergency device. It doesn’t alert a family member, a carer or anyone else if a call goes unanswered — nobody is watching on the other end. If you need someone to know a reminder was missed, you need a person or a monitoring service, not this.
For critical medication, treat any reminder — call, alarm, or app — as one layer only, and pair it with something that verifies the dose actually happened: a weekly pill organiser you can see at a glance, or a person who checks.
If the free fixes above solved your problem, you don’t need any of this. A correctly configured phone is a perfectly good reminder system, and it’s free.