A sensor that stops reporting is almost never broken. In most cases it is one of a short list of ordinary problems, and the order below goes from the most common to the least. Start at the top.

First, read what the dashboard says

Open the device page. If the device syncs from a brand's cloud, a failed sync shows a message in plain language near the top, such as a refused login or a provider outage. That message usually names the cause. If the device pushes its own data, the page shows when the last reading arrived. A reading from three days ago and a reading from three minutes ago point to very different problems.

Batteries

This is the cause far more often than anything else. A sensor with weak batteries can keep its display alive while no longer having enough power to transmit. Cold makes it worse, because batteries deliver less in low temperatures, which is why sensors tend to fall silent on the first frosty night.

  • Replace the batteries with fresh ones of the type the maker recommends.
  • For outdoor sensors in cold climates, lithium cells usually last through winter better than alkaline ones, if the maker says they are allowed.

Distance and obstacles

Radio sensors that talk to a gateway have a real range, and walls, metal roofs and water pipes cut it. If a sensor worked in the kitchen but not in the shed, try moving it closer to the gateway for a day. If it comes back, you have found the limit.

Wi-Fi

  • 2.4 GHz only. Most sensors and hobby boards cannot use 5 GHz networks. If your router merges the two bands under one name, some devices struggle to join.
  • A changed password or router. The sensor still has the old details and keeps trying forever. It needs setting up again.
  • Signal strength. A sensor at the edge of your Wi-Fi may connect fine for weeks and then drop out when something changes in the room.
  • Power cuts. After an outage the router can take longer to come back than the sensor, and some devices give up instead of retrying.

The gateway or hub

If several sensors went quiet at the same moment, look at what they share. That is nearly always the gateway. Check that it is powered, that its light shows a network connection, and unplug it for ten seconds to restart it.

The brand's cloud

For sensors that sync from a manufacturer's cloud, the manufacturer's service can have an outage or change how its login works. Open the brand's own app. If it shows no recent data either, the problem is upstream and will clear on its own. If the app has data but SensorConsole does not, the device page error message tells you what to fix. A refused login usually means an API key was replaced or revoked, and you need to add the device again with the new key.

For boards you programmed yourself

DIY boards add a few causes of their own.

  • Brownouts. A weak power supply or a long thin USB cable makes a board reset when the Wi-Fi radio transmits. If the board restarts in a loop, try a different supply.
  • No reconnect code. A sketch that connects to Wi-Fi once in setup and never checks again will go silent after the first router restart. Check the connection each time through the loop.
  • Sending too fast. SensorConsole accepts one reading per device every 10 seconds. Anything faster gets a reply with code 429. Send every 5 minutes or slower.
  • A wrong token. A reply with code 401 means the token in your code does not match the device. Copy it again from the device page, with no spaces on either side. Many wrong tries in a short time from one address pause that address for ten minutes.
  • Print the reply. Make your code print the response code from the server. It turns a silent failure into a clear message.

Let the dashboard tell you next time

On the device page, open the Alerts box and set Email me if this device goes silent for more than to a number of hours that suits the sensor. A sensor that reports every minute can use 2 hours. One that reports every hour should use 6 or more. You hear about the next failure the same day, not when you happen to look at the chart.