London calls don’t pause just because the Tube does. Signal-Safe Journeys is my Sunday-Spec for Citymapper: a new “connectivity” filter that maps only routes with continuous 4G or station Wi-Fi, shows a live countdown to the next black-spot, and gives a gentle buzz 30s before signal drops. Pair it with an OOH train-into-signal-bars visual and commuters stay on the line—literally and figuratively.