Did you just upgrade to the new version of the App? Offline is a "new" state for the sensors. While I do not know the Securifi definition (what their code says needs to happen to display it) it seems to match up with sensors that do not regularly report their state or have lost power.
I have MANY sensors that do not regularly report (switches, motion detectors, etc...) that show as offline. But when the motion detector is triggered and reports back, the Almond still displays it and it is no longer listed as offline. Same for switches. Sensors that are regularly reporting back still seem to show up normally.
So far it appears useful. It clued me in to a window sensor that had reported low battery but is no longer reporting at all (they usually take a while to die completely and I like to get the last bit of juice out of those batteries).
