Honeywell 7939-2 Frequently Asked Questions

What Are Door Contacts?
Sensors that are used to monitor whether a door is opened or closed are often called door contacts. Learn about door contacts and how they are used with alarm systems.
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What Do Normally Closed and Normally Open Mean?
"Normal" is the normal state of an opening, such as a door. Normally open/closed refers to the state of a contact connected to a door in its normal position.
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