Answer: By sending an alert to your smartphone.
The Inrigo waterproof camera backpack is prepared for the unfortunate possibility that it might not always be able to keep your stuff dry. Say you didn’t correctly close the pack to ensure a waterproof seal, or you put something away that wasn’t fully dry. Rather than just waiting for you to open up the pack hours later and discover your mistake, and the potential repercussions, the Inrigo can let you know that something isn’t right.
That’s because the pack contains an internal humidity sensor that can communicate via Bluetooth with an iOS/Android app. When it detects moisture in the bag, it can send an alert to the app on your smartphone. You can also set the level of humidity at which it will send an alert, so if it's not serious, you won’t be bothered. You will also be alerted if you get too far away from your bag. Just remember not to put your phone in the bag.
Check out the Inrigo Kickstarter campaign page here.