[General] when the emergency happens or when an emergency happens.

[arjitsharma]

Can I say both the following?
1. Call me when the emergency happens.
2. Call me when an emergency happens.

 

[Rover_KE]

Only use those sentences if you are both expecting an emergency to occur.

Normally 'Call me in an emergency' is sufficient.

 

[arjitsharma]

Are one of the two sentences incorrect?

 

[andrewg927]

1 means you are referring to a specific situation where an emergency could occur. 2 just means any emergency.

 

[GoesStation]

Can I say both the following?
1. Call me when the emergency happens.
2. Call me when an emergency happens.

Are one of the two sentences incorrect?

Number 1 is wrong. "If" would be more appropriate than "when" in number 2.

 

[Rover_KE]

[STRIKE]Are[/STRIKE] Is one of the two sentences incorrect?

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[Lynxear]

Can I say both the following?
1. Call me when the emergency happens.
2. Call me when an emergency happens.

Both are correct but it depends on context.

1. Call me when the emergency happens.

This sentence applies when referring to a specific emergency. The speaker knows the emergency will happen sometime. He just does not exactly when.

2. Call me when an emergency happens.

This sentence applies is a situation where emergencies are possible. The speaker is a person who must be alerted when any emergency happens. He is giving instructions to keep him informed when/if an emergency ever occurs.