Do you have a leterbox?
Is your letterbox on remote place place?
Are you renting a property, but letterbox is still yours?
With letterbox sensor you are able to:
Get email or SMS, if new mail in the letterbox
Get email or SMS, if letterbox is emptied
Get approximate number of letters inside
Easy to install to most of retail letterboxes
sigfox network compatible
More than 1-3 years on battery (2xAAA)