Alert thresholds
A threshold (alarm limit) is the range a single tag is allowed to be in. When a reading goes outside it, the device's status dot turns yellow, the device shows an Alert badge and a THRESHOLD_VIOLATION alert is recorded. When the reading returns to range, a THRESHOLD_CLEARED alert is recorded and the dot goes back to green.
Alerts fire only on the crossing — once when the value leaves the range and once when it comes back — not on every reading, so you won't be flooded while a value sits out of range.
Setting or changing a threshold
Open the device and find the tag.
Edit its alarm limit and choose a mode:
Mode Alarms when the reading is… Typical use Alarm above above the limit oil temperature, pressure, nitrate Alarm below below the limit tank level, battery, dissolved oxygen Alarm outside outside a low–high range supply voltage, pH Alarm beyond ± further than ± the limit from zero tilt, levelling No alarm never — the tag is recorded but not alarmed on Optionally add a Watch value (an early warning inside the limit) and a hysteresis — see Normal, Watch and Alert.
Save. The change takes effect on the next reading.
You can edit a threshold at any time without deleting and re-adding the tag. Choose No alarm to remove it.
Enter thresholds in displayed units. If the tag has a scaling factor (multiply or divide) or offset (see device parameters), type the values as they appear on your dashboards — i.e. after scaling is applied, not the raw sensor number. Each raw reading is converted to the displayed value before it is compared to the limit, so a limit of
45matches when the shown value crosses 45.
Plan feature. Setting an alert threshold requires a plan that includes thresholds. On plans without it, the threshold fields are disabled — upgrade to enable them. (You can always set a tag back to No alarm.)
Where the comparison happens
Behind a Synacl ESP32 gateway, the gateway compares readings itself, so it alarms even while its uplink is down — and saving a limit pushes the new configuration to the gateway. Every other device — polled by Synacl, webhook, direct MQTT, or behind a software or third-party gateway — is compared in the cloud as each reading arrives. The Alarms evaluated setting on a device's page shows which applies and lets you switch a gateway device; switching restarts the gateway once. Details in Normal, Watch and Alert.
Threshold vs. rules
A threshold gives you the at-a-glance yellow dot, the Watch/Alert badge, a place on the Active alarms page and a recorded event. For actions when a value crosses a limit (email, webhook, in-app, MQTT), create an alert rule instead — rules add delivery and cooldown on top, and a rule's threshold is set separately from the tag's limit.