Many posters have problems hooking up to WiFi. Distance often is part of the problem. But also what is in that distance. I read posts about someone cannot hook up although they are only 6 feet from their router. Then several posts later they write that 6 feet includes an interior wall, a hallway, an exterior wall (composed of drywall, insulation, and aluminum siding).
Those walls attenuate the signal a lot more than 6 foot of clear air across the living room.
/edit - (thanks to DreadPirateRush)
For the 2.4GHz camera wi-fi a “wi-fi analyzer” app will give you a good idea of signal strength.
However with the Sense it operates on 915MHz, and I have not found a free Android app to measure that signal strength,
What you state is the reason nobody can give a firm answer to how far a wifi signal will be usable. In general, direct line of site should provide at least 100’ range. But it depends on the transmitting antenna, receiving antenna, wifi band, wifi protocol, intervening obstacles (as you have noted). Way too many variables for a single definitive answer.
This is why when someone is having trouble with connecting that I suggest they use a WiFi analyzer app to check signal quality as well as the strength. Netgear’s “Wifi Analyzer” is one of my favorites.
Sorry! Your original post didn’t mention the sensors, so I answered as if you were referring to cameras themselves. And no, the sensors communicate with the bridge, and then the bridge uses the camera’s WiFi connection.