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An expression is a piece of code which retrieves the current state or setting of a device. For example, you could create an expression to fetch the current ‘on/off’ state of a light switch or the current temperature of your thermostat. The value returned by an expression may be Boolean (True/False) or an integer (numerical value) depending on the capability of the target device.

The following image shows an expression called ‘My Thermostat Expression’ which captures the current temperature from a physical thermostat device:

You can then use the result of this call in a meshbot trigger to determine whether or not an action runs. For example, the following meshbot turns on a lounge fan if the temperature captured by the ‘My Thermostat Expression’ hits 64 F:

You can use the value of an expression:

  • As a trigger node (left-side of the trigger). This simply uses the current value of the device referenced in the expression as the criteria for the trigger.

    E.g. – if ‘Device Expression Value’ = ‘Value X’ then turn the trigger true.

  • As a comparison data-point in the right-side of the trigger. This lets you compare the value of the device referenced in your expression with values from a different dewvice in the left side of your trigger.

    E.g. – if ‘Water Leak Sensor’ > ‘Water Leak Temperature’ ≠ ‘Device Expression Value’ then turn the trigger true.

Create an expression

In this example, we will create an expression that fetches the ‘On/Off’ status of a light switch. We will then show how to select the expression in a meshbot trigger.

  • Click ‘Automation’ > ‘Advanced Scripting’ > ‘Expressions’ > ‘Add New Expression’:
  • Type a name for your expression. This is the name that appears in your meshbot trigger if you select ‘Expression’.
  • Best practice is to name the expression after the device capability whose state you want to monitor. For example, ‘Dimmer Light Luminance’, ‘Thermostat Temperature’ or ‘Kitchen Door Lock Status’.
  • Important – Type ‘return’ at the start of the text field. You must always enter this command as a prefix in order for the expression to save correctly.
  • Next, choose the device and device capability whose status you want to monitor then click ‘Add Device Reference’ to create your expression:
  • This will automatically populate the text field with the code for your expression. Click ‘Create’ to save your expression:
  • After saving’, your expression will be listed in the ‘Expressions’ area as shown below:
  • You can now select your expression by name in a meshbot trigger. You can use the values it returns as a simple trigger node or as a point of comparison with the value/status of another device: