I spent some time looking for a Z-Wave sensor for my backyard gate. I didn't find much for something that was rated for outdoors and all weather so I made my own.

The key here is utilizing my favorite Z-Wave Door Sensors by EcoLink because they have an internal connection for wired sensors allowing you to connect almost anything to these. I was able to find a heavy duty stainless steel garage door contact sensor and I was off and running.

You'll want to enclose your Z-Wave Door Sensor in something that is rated IP65 or higher to protect it from the elements. I went with this sealed project box here that was just deep enough for the sensor and mounted nicely on my 4" fence post.

Drill a hole in your enclosure to pass the armored cable from the sensor and attach it to the contacts inside your Z-Wave sensor. It's a little messy, but I used some outdoor sealant to seal up the cable entrance into the enclosure.

Install the cover back onto the enclosure with the gasket seal. I like to treat it like lug-nuts on a tire and tighten each one in a diagonal fashion to ensure an even seal around the enclosure.

Mount the contact sensor near your gate opening and attache the magnet and bracket (if needed) to the gate.

What I really like about this garage door contact sensor is that it has a 3" open gap where it will still read as closed. You can mount the magnet on the gate door in such a way that it isn't visible from the outside and it made for a very clean and covert installation.

Now the fun part, I will presume you know how to include the Z-Wave sensor in your network. I use Home Assistant for all of my home automation needs. I like to use template sensors to make my Door Sensors make a little more sense to me in the frontend:

sensor:  
  - platform: template
    sensors:
      backyardgatestate:
        value_template: '{% if 
        is_state("binary_sensor.ecolink_doorwindow_sensor_sensor_14_0", "off") %} 
        Closed
        {% else %}
        Open 
        {% endif %}'
        friendly_name: 'Backyard Gate'

And now we can create automations based off of the gate such as an alert notification or turning on some exterior lighting in your backyard!

automation:  
  alias: Notify iOS app backyard gate was opened
  trigger:
    platform: state
    entity_id: binary_sensor.ecolink_doorwindow_sensor_sensor_14_0
    to: 'on'

  action:
    service: notify.ios_iphone
    data:
      message: "Backyard Gate is open!"
      data:
        attachment:
          content-type: jpeg
        push:
          category: camera
        entity_id: camera.backyardcamera

Hope this helps someone out! Sometimes it's very easy to build it when a specific device does not exist!