PRTG Manual: Sensor States

In the PRTG device tree, you usually create several sensors for each device. With sensors, you can monitor different aspects of your devices. Using a color code, they always show you what is going on in your network.

The color of a sensor always 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 summarized sensor states are shown (in the device tree, or on geographical maps): the higher a status is in the hierarchy, the higher is its priority regarding the display of sensor states. For example, if all the sensors of a specific device are Up, but one of its sensors reaches a Down status, then the overall status of this device is Down as well (for example, displayed in red in the Tree Map 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 Warning and Down Behavior below 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 that was set in the Sensor Channel Settings, or a Down status because of a sensor 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 node reports this sensor as Down, while at least one other 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 by a PRTG user via the Acknowledge Alarm function. This can be helpful to indicate that an alarm has already been brought to attention. For acknowledged alarms, no further notifications are sent. To show this sensor 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 has detected an error and shows a Warning status, but PRTG tries to reach the monitored device again. The sensor may soon change to a Down status. See section Sensor Warning and Down Behavior below for more information. Another reason for a Warning status can be a warning limit set in a sensor's Sensor Channel Settings.
Orange	Unusual	The sensor reports unusual values for this weekday and time of day. The unusual detection is based on the sensor's historic average data and can be configured or disabled in the system administration. You can also disable unusual detection for certain groups (see Group Settings).
Green	Up	The last scan was okay and the sensor is currently receiving data.
Blue	Paused	The sensor is currently paused (for a certain time span, indefinitely, or triggered by 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 show this status persistently, a PRTG restart may be necessary. For extended troubleshooting, see the Knowledge Base: What to check if sensors are gray?

Sensor Warning and Down Behavior

The Down status symbolizes that something is wrong with a monitored 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 recontact the device before setting a sensor to a Down status (this is true for almost all types of 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 monitoring object. 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.

The behavior described does not apply to Warning or Down states that are activated because of a warning or error limit set in the Sensor Channel Settings or to channels using lookups.