Get notified if there are X number of unknown PRTG sensor

PRTG has different sensor states. They are represented in different colors. For example, green means healthy, red means there is a problem, and orange means unusual activities in the network. This article focuses on unknown sensors, but it can be used for any other sensor state.

I will show you how you can monitor the number of unknown sensors, and get notified if the threshold is reached.

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Step 1: Add the target PRTG core server as a device

In the first place, you need to add a new device with the IP or DNS of your PRTG core server. You can add it to your existing PRTG core server.

Step 2: Add HTTP XML/REST Value sensor

The HTTP XML/REST Value sensor retrieves an .xml file from a URL and parses it. In this case, you use it to query your PRTG core server and check what is the number of unknown sensors. Navigate to your target PRTG core server device.

1. Add HTTP XML/REST Value sensor.
2. Change the name of the sensor (optional). In my case, it is Unknown sensors.
3. Type URL

http://PRTGCoreserver_IP/api/gettreenodestats.xml?username=jasmin&passhash=1234567890

4. Type XML Node (and optional property)

undefinedsens

5. Type the HTTP User Name and HTTP credentials that have permission to query the PRTG core server. You can also create a dedicated API user for that purpose. In the end, it should look like

6. Type %1 into Custom Message so the sensor only shows a number of unknown sensors without any strings.
7. Click Create.
8. Congratulation. Your sensor is up and running. In my case, it shows 31 as a number of unknown sensors on the target PRTG core server.

Step 3: Enable channel limits

In the second step, you need to configure limits, so the sensor goes to a down state if a certain number of the unknown sensor is detected.

1. Navigate to your sensor.
2. Click on settings as shown in the screenshot below, or click on sensor channel Value.

3. Under Lookups and Limits, click on Enable alerting based on limits, and under Upper Error Limit type a number of sensors.

In my case, it is 30. If there are 30 unknown sensors, this sensor will go downstate. Once you save changes, the sensor gauge will change color.

Step 4: Configure notifications

In the last step, you need to create a notification, so PRTG informs you if there are any changes with your sensor.

1. Navigate to your sensor.
2. Click on Notification triggers.
3. Create Add State Trigger notification and configure what kind of notification you want to receive in case there is X number of unknown sensors on your PRTG Core server. I go with simple Ticket notification.

The sensor goes into the down state because there are 33 unknown sensors.

I received the ticket after 30 seconds. You see that sensor is in a down state because there are 33 sensors in an unknown state.

Thank you for reading this article. If you found it useful, feel free to share it with your network.