changed

Execute the rule when an item, group, member of group, or thing changed state.

Syntax:

changed entity [from:] [to:] [for:]

Options	Description	Examples
`entity`	One or more item, group, member of group, or thing to monitor for changes	`changed SwitchItem1` `changed Switches.members`
`from:`	Optional: Only execute rule if previous state matches from state(s)	`from: OFF` or `from: 4..9`
`to:`	Optional: Only execute rule if new state matches to state(s)	`to: ON` or `to: ->t { t.even? }`
`for:`	Optional: Only execute rule if value stays changed for duration	`for: 10.seconds`

The from and to options are enhanced compared to the rules DSL:

from and to accept arrays to match multiple states.
If the changed element being used as a trigger is a thing, the to and from values will accept symbols and strings, where the symbol matches the supported status
Support for ranges
Support for procs/lambdas for complex state matches

Changed Duration

The for parameter provides a method of only executing the rule if the value is changed for a specific duration. This provides a built-in method of only executing a rule if a condition is true for a period of time without the need to create dummy objects with the expire binding or make or manage your own timers.

For example, the code in this design pattern becomes (with no need to create the dummy object):

rule "Execute rule when item is changed for specified duration" do
  changed Alarm_Mode, for: 20.seconds
  run { logger.info("Alarm Mode Updated")}
end

Examples

Multiple items can be separated with a comma:

rule 'Execute rule when either sensor changed' do
  changed FrontMotion_Sensor, RearMotion_Sensor
  run { |event| logger.info("Motion detected by #{event.item.name}") }
end

Or in an array:

SENSORS = [FrontMotion_Sensor, RearMotion_Sensor]
rule 'Execute rule when either sensor changed' do
  changed SENSORS
  run { |event| logger.info("Motion detected by #{event.item.name}") }
end

Group member trigger:

rule 'Execute rule when member changed' do
  changed Sensors.members
  run { |event| logger.info("Motion detected by #{event.item.name}") }
end

for parameter can be an item too:

Alarm_Delay << 20

rule "Execute rule when item is changed for specified duration" do
  changed Alarm_Mode, for: Alarm_Delay
  run { logger.info("Alarm Mode Updated")}
end

You can optionally provide from and to states to restrict the cases in which the rule executes:

rule 'Execute rule when item is changed to specific number, from specific number, for specified duration' do
  changed Alarm_Mode, from: 8, to: [14,12], for: 12.seconds
  run { logger.info("Alarm Mode Updated")}
end

Works with ranges:

rule 'Execute rule when item is changed to a range of numbers, from a specific range of numbers, for specified duration' do
  changed Alarm_Mode, from: 8..10, to: 12..14, for: 12.seconds
  run { logger.info("Alarm Mode Updated")}
end

Works with endless ranges:

rule 'Execute rule when item is changed to any number greater than 12'
  changed Alarm_Mode, to: (12..)   # Parenthesis required for endless ranges
  run { logger.info("Alarm Mode Updated")}
end

Works with procs:

rule 'Execute rule when item state is changed from an odd number, to an even number, for specified duration' do
  changed Alarm_Mode, from: proc { |from| from.odd? }, to: proc {|to| to.even? }, for: 12.seconds
  run { logger.info("Alarm Mode Updated")}
end

Works with lambda procs:

rule 'Execute rule when item state is changed from an odd number, to an even number, for specified duration' do
  changed Alarm_Mode, from: ->from { from.odd? }, to: ->to { to.even? }, for: 12.seconds
  run { logger.info("Alarm Mode Updated")}
end

Works with things as well:

rule 'Execute rule when thing is changed' do
   changed things['astro:sun:home'], :from => :online, :to => :uninitialized
   run { |event| logger.info("Thing #{event.uid} status <trigger> to #{event.status}") }
end

Real world example:

rule 'Log (or notify) when an exterior door is left open for more than 5 minutes' do
  changed ExteriorDoors.members, to: OPEN, for: 5.minutes
  triggered {|door| logger.info("#{door.id} has been left open!")}
end