Hi fillibar,
The wall is metal, but the door is always wide open. Wifi signals are robust (thank you Almond!). But the light switch is only 20 feet (10feet, then a left turn through the doorway and another 10feet line of sight to the light switch) from the master router (and 3 feet from a slave A3 ... can't wait till the slaves can also host a zWave dongle!). The Almond phone app will actually - with a noticeable delay - 'work' once on the light switch 'smart device' on/off toggle one time, but then will get caught in a relentless "updating sensor" loop.
The Peanut plugs are bulletproof - don't understand why no one makes (or do they?) a zigbee in-wall light switch, and the heck with the zWave technology.