Intransitive use of the verb to trigger

Solution 1:

As I was interested in which dictionaries give the intransitive definition, I checked a few:

Here are the ones that don't list an intransitive use:

• Oxford Living Dictionaries
• American Heritage Dictionary
• Collins Dictionary
• Cambridge Dictionary
• Macmillan Dictionary
• wiktionary.org (Surprised me, as I thought this was a very permissive one)

Dictionaries that DO list an intransitive definition:

Random House Kernerman Webster's College Dictionary:

6. to release a trigger.
   
7. to become active; activate.
   

Merriam-Webster Dictionary:

to release a mechanical trigger

Random House Unabridged Dictionary (From dictionary.com):

7. to release a trigger.
   
8. to become active; activate.
   

Dictionaries I couldn't check because I don't have an account or subscription:

• OED
• Macquarie Dictionary

Whether you can use a verb intransitively or not is a tricky subject.

Solution 2:

Dictionary.com cites the intransitive usage:

Trigger:

verb (used without object)

1) to release a trigger

2) to become active; activate.

From: The CNC Toolbox: Computer Numerical Control

The alarm triggered when some switch contact opened a normally closed alarm circuit.