How to check total number of connected devices in IoT hub

jb_devel 120

Hello,

First Im not a cloud engineer and we currently dont have one as of the moment so this is a problem for us.

I would like to ask how to check the number of active devices currently connected to our IoT hub. Our devices reboots randomly everyday and im sure its sending some message to azure when it reboots.

Thank you!

Manas Mohanty 745 Reputation points Microsoft Vendor

2025-02-10T02:25:17.6233333+00:00

Hi jb_devel!

Hope the provided pointers have resolved your query.

Could you please upvote any answer.

Thank you.

2 answers

Manas Mohanty 745 Reputation points Microsoft Vendor

2025-02-04T05:57:51.1033333+00:00
Hi jb_devel!

Welcome to Azure IOT Q and A forum. Thank you for posting your query here.

To see connected Devices on IOT Hub

You can go to "monitoring" section from Azure IOT Hub resource in portal.azure.com

View metrics - then select "Connected Devices" and select a time span as scope

Reference on Metrics

You can set up a trigger alert based on device count metric

Reference on triggering alert

You can opt for "event grid" if you want to tune in device reboots, connects etc. as it provides low latency compared to Azure Monitor.

Reference on per event grid

Please don't forget to upvote this answer if it is useful to you.

Thank you.
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jb_devel 120 Reputation points

2025-02-04T07:35:24.3566667+00:00

@Manas Mohanty

Thank you for your response.

Is it also the same as the condition connectionState = 'Connected' in the iot hub query?

Thank you.

Manas Mohanty 745 Reputation points Microsoft Vendor

2025-02-05T01:31:52.9833333+00:00

Hi jb_devel!

Sorry for the delay in response.

Yes, connectionState = 'Connected' query will show devices in connected state but It has some limitations.

The connection state is updated only for devices that use MQTT or AMQP.

Updates to this property rely on protocol-level pings and may be delayed as much as five minutes.

IoT solutions shouldn't query the field at run time. For example, don't query the connectionState field to check if a device is connected before you send a cloud-to-device message or an SMS.

I think, it would be better to follow "digital twin" approach mentioned by Sander van de Velde | MVP in below thread to check realtime status of devices.

Thank you

jb_devel 120 Reputation points

2025-02-05T02:42:18+00:00

Hello @Manas Mohanty

Thanks for your feedback.

-Our devices uses MQTT.

-The approach he mentioned is quite difficult for me to understand.

-I asked him regarding the metrics Ive seen with regards to point results. Our develop environment has 1 active device as of the moment but why the metric has some point (0.9, 0.7 etc)results. Image below for your reference.

Thank you.

Manas Mohanty 745 Reputation points Microsoft Vendor

2025-02-05T13:35:36.47+00:00

Hi jb_devel!

Please change the time span to 30 mins or 1 hour to see real device count.

Thank you.
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Sander van de Velde | MVP 35,091 Reputation points MVP

2025-02-04T10:32:14.6666667+00:00

Hello @jb_devel ,

welcome to this moderated Azure community forum.

the Azure IoT Hub shows metrics about the number of devices being connected.

This metric is not real-time, it is updated once every few minutes. And it does not show a reliable history of connections/disconnections.

On the other hand, the IoT Hub exposes non-functional events about devices:

There are events for creating and deleting devices, for changes to the device twin, and connectivity.

Check this blog post about the details on how to configure this via the routes.

It references the deprecated TimeSeries Insights service but you can also route the messages to the free Azure Data Explorer (or a paid one with an SLA) via a stream analytics job and an eventhub.

This stream analytics job is needed because the details of the connection state and the device name are in the application properties. The Azure Data Explorer is not capable of exposing application properties in the database.

Therefor, the application properties should be moved to the actual message body.

As @Manas Mohanty mentioned, the IoT Hub also exposes EventGrid events for this.

If this is too complex at this moment, you can start with routing the events to a blob file in a storage account.

If the response helped, do "Accept Answer". If it doesn't work, please let us know the progress. All community members with similar issues will benefit by doing so. Your contribution is highly appreciated.
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jb_devel 120 Reputation points

2025-02-05T00:17:33.47+00:00

Hello @Sander van de Velde | MVP ,

Thank you for your response.

I have read your blog post and its impressive. However, its too much for me to comprehend since I do not have prior knowledge to cloud services.

I saw similar messages in our iot hub when performing basic query like the one I replied to Manas. I checked the metrics and provide filter of connected device.

My question is why the metrics shows a result of 0.60, 0.80, 0.40 etc? In this environment we have one device connected so it should show 1 or 0. Image below for your reference

Thank you.

Sander van de Velde | MVP 35,091 Reputation points MVP

2025-02-05T12:24:40.35+00:00

Hello @jb_devel ,

Think big, act small ;-) Yes, to work with these services, you need to build up some knowledge but starting with the metrics is ok.

The Metrics of the IoT Hub are built for scale so I think they take both timespans and number of connected devices into account.

This can lead to these 'strange' numbers.

An alternative is working with a Stream Analytics job and counting the number of (connected) devices per time window.

Azure Stream Analytics is perfect for looking at data in-flight.

Again, this means you need to invest some time to know the tool.

jb_devel 120 Reputation points

2025-02-06T00:30:59.6266667+00:00

Hello @Sander van de Velde | MVP ,

Thank you for your response.

I can confirm that we are currently have a Stream Analytics job running in this environment but I am not sure where to look at, could you please point me to the right section where I can view the number of connected devices.

Thank you very much.

Sander van de Velde | MVP 35,091 Reputation points MVP

2025-02-06T19:16:55.3433333+00:00

Hello @jb_devel ,

there are no metrics in the job, you need to created them yourself.

Write a custom script for this and at it to the rest of the script in the job.

It should count the distinct number of deviceID per time window based on the incoming messages. If you compare this with the number of actual devices.Perhaps this more elaborate example helps you too.
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