Those things are a very low power transmitter so even though it sez up to 100' that distance is clear line of sight distance. Start putting obstacles in that path then the distance will get shorter. Yeah, it'll transmit through walls, but the type of wall will have an effect, like is it a brick wall, a wood frame wall or a steel wall. And then what is inside the wall, electrical & plumbing will interfere. Your electrical circuit box will likely interfere as does air conditioning because that is 220 volts. Just a few things to consider.