Help for lock with storm door

A quick learner from USA says:

My 91 yr old mother likes to look out her storm door. For security she needs to be able to lock this door from the inside. But I need to be able to unlock the door from the outside with a key, especially if there is a medical emergency.
Is there such a setup and could you supply me the catalog numbers?
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Paul from SWISCO responded:
Thanks for posting. If possible, I'd like to see a picture of the handle set you are currently using. That will help us find the best way to satisfy your request. Specifically, we will need to see the inside and outside of the handle. I will also need the distance between the installation hole centers.
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