<%NUMBERING1%>.<%NUMBERING2%>.<%NUMBERING3%> 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 simple 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 below table, you will 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 geo maps): the higher a status is in the hierarchy, the higher will be its priority in displaying 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 will be Down as well (for example, displayed red in the Tree Map View), because this status is higher up in the hierarchy.

icon-i-roundDown and Down (Partial) states are equal in the status hierarchy.



Status Name





  1. PRTG is unable to reach the device, or the sensor has changed to the error state. See the Sensor Warning and Down Behavior below for more information.
    icon-i-roundBy design, a sensor does not record any data in its channels while it shows this status.
  2. Another reason for this status can be an error limit that is set in the Sensor Channels Settings, or an error status due to a sensor Lookup.
    icon-i-roundIn this case, the sensor continues to record data in all sensor channels although the sensor shows an error.



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.

icon-i-roundThis status is not available for sensors on remote probes in a failover cluster.



Down (Acknowledged)

The sensor is Down and the status was acknowledged by a PRTG user, applying the Acknowledge Alarm function. This can be helpful to mark that an alarm has already been brought to attention. For acknowledged alarms no further notifications are sent. To set this sensor status, right-click the sensor in Down status and from the context menu, select Acknowledge Alarm.... Then enter a comment and click OK.




The sensor gives an error reading, but PRTG will try again. The sensor may soon change to a down status. See the Sensor Warning and Down Behavior below for more information. Another reason for this status can be a warning limit set in a sensor's Sensor Channels Settings.




The sensor reports unusual values for this weekday and time of day. The unusual detection is based on the historic average data and can be configured or disabled in the system administration. You can also disable unusual detection for certain groups only (see Group Settings).




The last scan was okay and the sensor currently receives data.




The sensor is currently paused (for a certain timespan, indefinitely, or triggered by a dependency).


Black (Gray)


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.

icon-book-bulbFor extended trouble shooting please see this Knowledge Base article: What to check if sensors are black (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 crashed server.

After a failed request, PRTG tries to re-contact the device before setting a sensor to Down status (this is true for almost all types of sensors):

  1. If a request to a device fails for the first time, the sensor will change to Warning status. PRTG repeats the request and attempts to re-scan the device immediately.
  2. If the second request also fails, the sensor changes to 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 informed promptly about any network issues.

icon-i-round-redThe behavior described above does not apply to Warning or Down states that are activated due to a warning or error limit set in the Sensor Channels Settings or to channels using lookups.


Video Tutorial: The PRTG Sensor States

Knowledge Base: What to check if sensors are black (gray)?


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Keywords: Down,Down (Acknowledged),Down (Partial),None,OK,Paused,Sensor,Sensor Behavior,Sensor Status,Unknown,Unusual,Warning