FireChat, that offline messenger that Hong Kong locals used during the height of their pro-democracy protests, now has off-the-grid private messaging capability. If you recall, you could only use its public "Nearby" tab if you want to talk to people in your area without depending on an internet connection. Now, you can contact someone in private -- provided that you're not the only two people using the app in your town. In order for the PMs to go through, messages hop on whatever's available: multiple local networks, WiFi, Bluetooth and even the internet. According to TechCrunch, FireChat uses the store-and-forward technique, wherein your message is sent to the nearest available network and kept there until the next one becomes available. Don't worry, though: PMs will be encrypted to prevent other users from reading them.