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  5. 3.8.6.3. Trigger 

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#  3.8.6.3. Trigger

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##  Property Name

TRIGGER

##  Purpose

This property specifies when an alarm will trigger.

##  Value Type

The default value type is DURATION. The value type can be set to a DATE-TIME
value type, in which case the value MUST specify a UTC-formatted DATE-TIME
value. Property Parameters: IANA, non-standard, value data type, time zone
identifier, or trigger relationship property parameters can be specified on
this property. The trigger relationship property parameter MUST only be
specified when the value type is [ "DURATION" ](/iCalendar-
RFC-5545/3-8-2-5-duration.html) .

##  Conformance

This property MUST be specified in the [ "VALARM" ](/iCalendar-
RFC-5545/3-6-6-alarm-component.html) calendar component.

##  Description

This property defines when an alarm will trigger. The default value type is
DURATION, specifying a relative time for the trigger of the alarm. The default
duration is relative to the start of an event or to-do with which the alarm is
associated. The duration can be explicitly set to trigger from either the end
or the start of the associated event or to-do with the "RELATED" parameter. A
value of START will set the alarm to trigger off the start of the associated
event or to-do. A value of END will set the alarm to trigger off the end of
the associated event or to-do.

Either a positive or negative duration may be specified for the [ "TRIGGER"
](/iCalendar-RFC-5545/3-8-6-3-trigger.html) property. An alarm with a positive
duration is triggered after the associated start or end of the event or to-do.
An alarm with a negative duration is triggered before the associated start or
end of the event or to-do.

The "RELATED" property parameter is not valid if the value type of the
property is set to DATE-TIME (i.e., for an absolute date and time alarm
trigger). If a value type of DATE-TIME is specified, then the property value
MUST be specified in the UTC time format. If an absolute trigger is specified
on an alarm for a recurring event or to-do, then the alarm will only trigger
for the specified absolute DATE-TIME, along with any specified repeating
instances.

If the trigger is set relative to START, then the [ "DTSTART" ](/iCalendar-
RFC-5545/3-8-2-4-date-time-start.html) property MUST be present in the
associated [ "VEVENT" ](/iCalendar-RFC-5545/3-6-1-event-component.html) or [
"VTODO" ](/iCalendar-RFC-5545/3-6-2-to-do-component.html) calendar component.
If an alarm is specified for an event with the trigger set relative to the
END, then the [ "DTEND" ](/iCalendar-RFC-5545/3-8-2-2-date-time-end.html)
property or the [ "DTSTART" ](/iCalendar-RFC-5545/3-8-2-4-date-time-
start.html) and "DURATION " properties MUST be present in the associated [
"VEVENT" ](/iCalendar-RFC-5545/3-6-1-event-component.html) calendar component.
If the alarm is specified for a to-do with a trigger set relative to the END,
then either the [ "DUE" ](/iCalendar-RFC-5545/3-