PRTG Manual: Sensor States

The color of a sensor shows its current status. In the table below, you find a list of states a sensor can show. This list also reflects the hierarchy of states whenever PRTG shows summarized sensor states (in the device tree, or on geographical maps): the higher a status is in the hierarchy, the higher is its priority regarding when and how PRTG displays sensor states. For example, if all the sensors of a specific device show an Up status, but one of its sensors changes to a Down status, then the overall status of this device is Down as well (for example, displayed in red in the device tree view), because this status is higher up in the hierarchy.

Down and Down (Partial) states are equal in the status hierarchy.

Color	Status Name	Meaning
Red	Down	PRTG is unable to reach the device or the sensor has detected an error. See section Sensor Behavior for Warning and Down States for more information. By design, a sensor does not record any data in its channels while it shows a Down status. Another reason for this status can be an error limit in the sensor channel settings, or a Down status because of a lookup. In this case, the sensor continues to record data in all sensor channels although the sensor shows a Down status.
Green/Red	Down (Partial)	In a cluster, at least one cluster node reports this sensor as Down, while at least one other cluster node reports the same sensor as Up. This status is not available for sensors on remote probes in a failover cluster.
Bright Red	Down (Acknowledged)	The sensor is Down and the status has been acknowledged via the Acknowledge Alarm function. This can be helpful to indicate that an alarm has already been brought to attention. For acknowledged alarms, PRTG does not send further notifications. To show the Down (Acknowledged) status, right-click the sensor that shows a Down status. From the context menu, select Acknowledge Alarm. Then enter a comment and click OK.
Yellow	Warning	The sensor detected an error and shows a Warning status, but PRTG is trying to reach the monitored device again. The sensor may soon change to a Down status. See section Sensor Behavior for Warning and Down States for more information. Another reason for a Warning status can be a warning limit in the sensor channel settings.
Orange	Unusual	The sensor reports unusual values for this weekday and time of the day. The unusual detection is based on the sensor's historic average data. You can configure or disable unusual detection in the system administration. You can also disable unusual detection for certain groups (see section Group Settings).
Green	Up	The last scan was okay and the sensor receives data.
Blue	Paused	The sensor is paused for a certain time span, indefinitely, or because of a dependency.
Gray	Unknown	The sensor has not received any data yet or there is an error in (network) communication, likely on the probe system. If sensors persistently show this status, you may need to restart PRTG. For extended troubleshooting, see the Knowledge Base: What to check if sensors are gray? and My sensors show an Unknown status after a PRTG core server restart. What can I do?

Sensor Behavior for Warning and Down States

The Down status symbolizes that something is wrong with a device. There can be various reasons for a Down status, for example, an interruption in the physical connection to the device, an internet connection outage, or a server that stopped working.

After a failed request, PRTG tries to contact the device again before it sets a sensor to a Down status (this is true for almost all sensors):

If a request to a device fails for the first time, the sensor changes to a Warning status. PRTG repeats the request and attempts to rescan the device immediately.
If the second request also fails, the sensor changes to a Down status by default until the device is reachable again. You can change this behavior in the scanning interval settings of any object in the device tree. PRTG tries to reach the device with every scanning interval.

This procedure gives devices and services the chance to recover from a momentary overload and prevents false alarms. Still, you are immediately informed about any network issues.

This behavior does not apply to Warning or Down states that result from warning limits or error limits in the sensor channel settings. This behavior also does not apply to channels that use lookups.