Trigger the send smd node when a gpio pin status changes


I want to send a sms with the nexmo send-sms node when the status of a GPIO pin changes from high to low. I have no idea how I can trigger the node.
I hope somebody can help me with a solution.
Thank you.

To avoid confusion you should delete this post as you posted twice and the other post has been answered!

I'll lock it to avoid confusion.