Why has my smart speaker stopped responding?
Because several separate things must all be working — the microphone, the network, the cloud service and the account — and the symptoms differ enough to identify which has failed.
How it actually works, which explains the failure modes. The device listens locally for the wake word, using on-device processing. Everything after that is sent to servers for speech recognition and response. So the device can hear you perfectly and still do nothing, because the part that understands you is elsewhere.
Diagnosing by symptom:
No light or reaction at all — the wake word is not being detected. Check the microphone mute switch, which is physical on most devices and easily knocked; check power; and check for background noise or distance.
It lights up but does not answer — it heard you and could not reach the service. This is a network or service problem, not a microphone one, and is the most informative symptom.
"I'm having trouble connecting" — network or cloud service.
It responds but cannot control a device — the speaker is fine; the smart home integration or the device itself has failed.
It responds to some requests and not others — a specific service or skill is unavailable, or the account linkage has expired.
What to check, in order:
Is the service itself down? Check a status page or whether others report problems. This is worth checking first, because a substantial proportion of sudden failures are outages, and troubleshooting your own equipment during one is wasted effort.
Is the network working on other devices?
Restart the speaker, then the router.
Check the device appears in its app, and whether it reports offline.
Check account linkage for services that expired and need re-authorising — music and smart home accounts disconnect periodically.
Check the Wi-Fi band. Some speakers support only 2.4GHz, and a router change or band-steering behaviour can leave them unable to connect.
Check for a firmware update that stalled.
Re-add the device as a last resort.
The underlying point: these devices depend entirely on a remote service and an active account. When the manufacturer discontinues a product's service, the hardware stops working — which has happened to several smart home products and is worth weighing before buying.