# DC Voltage measurement

**URL:** <https://forum.ewelink.cc/t/dc-voltage-measurement/21360>\
**Category:** Free discussion\
**Created:** [September 2, 2023, 10:46pm UTC](https://forum.ewelink.cc/t/dc-voltage-measurement/21360 "2023-09-02T22:46:38Z")\
**Posts on this page:** 1\
**Showing post:** 3

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**Author:** ![euv](https://dub1.discourse-cdn.com/flex005/user_avatar/forum.ewelink.cc/euv/32/1508_2.png) [@euv](https://forum.ewelink.cc/u/euv)\
**Post date:** [September 4, 2023, 6:42pm UTC](https://forum.ewelink.cc/t/dc-voltage-measurement/21360/3 "2023-09-04T18:42:09Z")

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Buy the Digital Voltage Control Relay Module, then you need to modify a smart door sensor that you will connect to the contacts of the relay module. Look here for such a module [https://vi.aliexpress.com/item/32977883482.html?gatewayAdapt=glo2vnm](https://vi.aliexpress.com/item/32977883482.html?gatewayAdapt=glo2vnm)  
I have described the modification of the door sensor in this topic  
[Trigger a device ( if lamp is offline) - #12 by euv](https://forum.ewelink.cc/t/trigger-a-device-if-lamp-is-offline/8575/12)

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