Any Ideas

I need to install a 12 volt system, to alert by alarm, when both security door are open at the same time.

1. I have a 2 door airlock.

2. A light is on in the airlock.

3. The light remains on when one door is open.

What I need is an alarm to sound when both doors are open ?

I haven't started the project yet, I would be grateful for any help.

List of materials and a diagram would be superb.

Many thanks in advance for any help.

Best regards

Paul,, (Hampshire, UK)