Direct answer
For the Fitbit Sense 2, phone permission, app-specific mirroring, Focus modes, Bluetooth and background sync should be separated. First, send a controlled text/app alert with phone locked.
What this covers
- Fitbit Sense 2 (FB521)
- Fitbit device; Google-account migration, onboard GPS, voice, ECG and charging cable vary.
- The specific fault this record addresses: notifications are missing or delayed
What it does not cover
- ×The same symptom on a different Fitbit product line, which has its own record and its own cited source
- ×An on-screen error code whose meaning has not been checked against this exact model's manual
- ×Live electrical, gas, sealed-system, internal battery-cell or structural repair — a technician boundary, not a self-service step
Differential
What actually causes this, and how to tell them apart
These are ordered by how often each one is the answer, not by how easy it is to try. The point of the middle column is that two causes producing the same headline symptom rarely produce the same detail — that detail is what tells you which one you have before you change anything.
- 1
A Focus, Do Not Disturb or bedtime mode is suppressing alerts
What separates it Notifications stopped at a certain time of day, or a moon/DND icon is showing on the watch or phone.
How to confirm Check for an active Focus/DND/sleep mode on both the watch and the phone, including scheduled ones; these silence forwarding exactly as configured.
- 2
The watch only mirrors when the phone is locked
What separates it Alerts reach the watch only sometimes, correlating with whether the phone screen was on.
How to confirm Many watches deliberately show a notification on the wrist only when the phone is locked or the app is not in the foreground; test with the phone locked to match real conditions.
- 3
A specific app's notifications are off on the watch or phone
What separates it Some apps come through and others never do.
How to confirm Enable the missing app's notifications on both the phone and the watch's mirroring list; an app muted on either side will not reach the wrist.
- 4
The Bluetooth link or background access dropped
What separates it Everything is delayed or stops until the watch reconnects to the phone.
How to confirm Confirm the watch is connected and the companion app has background access; a dropped link or a backgrounded app delays or halts notifications.
Before you touch a setting
Record this first — changing settings destroys the evidence
Every item below stops existing the moment a reset, re-pair or settings change is made. Written down first, they are what separates the causes above; recovered afterwards, they are guesswork.
- Whether a Focus/DND/sleep mode is active on the watch or phone.
- Whether it affects all apps or only specific ones.
- Whether alerts arrive with the phone locked, unlocked, or only after reconnecting.
Send a controlled alert with the phone locked
ReversibleReproduces the exact condition the watch mirrors under.
Check Focus/DND/sleep modes on both devices
ReversibleThese suppress forwarding on a schedule and are easy to miss.
Enable the needed apps on both phone and watch, and restore the link/background access
ReversibleAn app muted on either side, or a backgrounded companion app, blocks alerts.
Repeat the locked-screen and reconnect tests to confirm
ReversibleVerifies delivery under normal and out-of-range conditions.
Model-specific
What is true of this model and not of its siblings
Generic advice for the product line fails here. Each item below is a property of this specific model family that changes which of the steps above apply to you.
- Model scope
- FB521. Fitbit device; Google-account migration, onboard GPS, voice, ECG and charging cable vary.
- Model — Sense 2 (health smartwatch)
- Fitbit's health-focused smartwatch with the most sensors: continuous EDA (all-day stress), ECG, skin temperature, blood oxygen and heart rate, plus built-in GPS. It has a MICROPHONE (for voice) but NO speaker — so voice input works, but it cannot play call audio; speaker/mic symptoms apply only to the mic side.
- No cellular
- No cellular — notifications and voice go through the connected phone. 'Cellular not working' does not apply.
- Body Response (cEDA)
- Its standout is continuous EDA stress tracking via the Body Response sensor; readings need good skin contact, so fit matters.
- Symptom boundary
- This record covers Fitbit Sense 2 when it notifications are missing or delayed. A different symptom on the same hardware, or this symptom on a different Fitbit product line, has its own record with its own causes and its own cited source.
Stop boundary
When this stops being a self-service repair
Continuing past any one of these costs more than the repair saves — in safety, in warranty, or in evidence a technician needs.
- !Take care not to disable emergency, security or health alerts while trimming notifications — keep those categories on.
Evidence ledger
Sources behind this answer
Visible sources support the visible claims. Home Product Support records the publisher, the fact used and the review date; community reports can suggest an issue but do not become a published fact on their own.
Where the manufacturer's article stops. Google Fitbit Help publishes this as "Why didn't my Fitbit device alert me?". Google's Fitbit notification troubleshooting article. Probed 2026-08-28: title-verified. What that article does not carry is the model boundary — it is written for a product line, and FB521 is the scope applied here. Where a control label, terminal, indicator pattern or reset sequence differs on your unit, the manual for that exact model is the authority, not this page and not the article.
Exact questions
Common follow-ups
Can I take calls on my Fitbit Sense 2?+
Not with audio on the watch — the Sense 2 has a microphone (for voice commands and quick replies) but no speaker, so it cannot play call audio through the watch. You can see and manage calls from your phone and use voice for replies, but you talk on the phone. So the speaker side does not apply; the microphone does. It also has no cellular, so it relies on your paired phone.
I only get some notifications on my watch, not all of them.+
Two things cause this most often. First, many watches only show an alert on your wrist when the phone is locked or the app is not open on screen — so test with the phone locked. Second, notifications have to be enabled for each app on both the phone and the watch's mirroring list; an app muted on either side never reaches the watch. Also check that no Focus, Do Not Disturb or sleep mode is quietly suppressing them on a schedule.
Does this answer apply to every Fitbit model?+
No. It is scoped to FB521. Fitbit device; Google-account migration, onboard GPS, voice, ECG and charging cable vary.
What should I record before troubleshooting notifications or alerts?+
Record the complete model identifier, exact message or indicator, software/firmware where visible, the operating stage and what still works.
Why is a factory reset not the first step?+
A reset can erase accounts, networks, maps, schedules or preferences without distinguishing notifications, alerts. The ordered checks preserve that evidence.
When should I stop and use qualified service?+
Preserve emergency, security and health alerts.
Answer for the exact device and software version shown above.