# OPC-UA subscription and event notification

**URL:** <https://forum.inductiveautomation.com/t/opc-ua-subscription-and-event-notification/16070>\
**Category:** Ignition\
**Created:** [November 21, 2017, 12:56pm UTC](https://forum.inductiveautomation.com/t/opc-ua-subscription-and-event-notification/16070 "2017-11-21T12:56:53Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![piero](https://avatars.discourse-cdn.com/v4/letter/p/b5e925/32.png) [@piero](https://forum.inductiveautomation.com/u/piero)\
**Post date:** [November 21, 2017, 12:56pm UTC](https://forum.inductiveautomation.com/t/opc-ua-subscription-and-event-notification/16070/1 "2017-11-21T12:56:53Z")

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I’m connecting to a prosys OPC-UA demo server and I’m defining OPC TAG.  
It is not clear from the manual if I’m realizing a subscrition to the OPC-UA node (i.e. I’m notified only when the value changes) or the node is polled.

Besides, the OPC-UA demo server is sending alarm, but I can not see them in IGNITION. How can I subscrive and receive server event in ignition?  
Please note that the simple OPC-UA client in ignition is able to subscribe and receive alarm and notification.  
Thanks,

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**Author:** ![Kevin.Herron](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/kevin.herron/32/7259_2.png) [@Kevin.Herron](https://forum.inductiveautomation.com/u/Kevin.Herron)\
**Post date:** [November 21, 2017, 2:11pm UTC](https://forum.inductiveautomation.com/t/opc-ua-subscription-and-event-notification/16070/2 "2017-11-21T14:11:12Z")

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If you’re in the designer and you drag and drop a tag from the OPC browser, that’s using a subscription (unless the scan class is in OPC Read Mode).

If you’re in the quick client on the gateway web page then clicking the [s] button next to each node will subscribe to that node for the duration of your web session.

Alarms and events are not supported in either context.

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**Author:** ![piero](https://avatars.discourse-cdn.com/v4/letter/p/b5e925/32.png) [@piero](https://forum.inductiveautomation.com/u/piero)\
**Post date:** [November 22, 2017, 9:13am UTC](https://forum.inductiveautomation.com/t/opc-ua-subscription-and-event-notification/16070/3 "2017-11-22T09:13:10Z")

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Thanks for your fast and clear answer.  
Piero