My idea is not for alarm purpose in the main, but to generate a code for a site to be used by call out staff to access a key locker.
So each site is different but call out staff eg security guards etc don't carry internal keys or codes for sites.
This is a customer specific.
If they attend a site they get code then access keys.
We can use different seed codes if needed for each site if they require in the future
Also just needs to be an app, not on server