Sorry to hear about the loss of your keys to the Sentry safe. Luckily, they have a relatively easy process to retrieve the key to your safe.
Here is what you need to do to get another key from sentryVisithttp://www.sentrysafe.com/CustomerCare/Need_A_Key
You will most likely need a notarized form, you can download one from the Website provided above.
Here is a copy of the notary form as well
This process is necessary in order to prove the ownership of you safe. You will be able to purchase 2 keys for $15 (including delivery) using standard delivery.
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