Completely hidden wireless networks?

I once read about someone who concealed a router on a wall and set up a completely hidden hotspot. Not just hiding the SSID - it supposedly didn't show up at all when scanning, so you had to know the network name, security and password in advance, and manually create a profile in your computer.

Is that actually possible? It seems too far-fetched for me since 1. I never saw an option to disable beacon frames on any router, 2. those are used by clients to know if you're still in range.

The closest thing I know to be feasible is using channel 14, which is only allowed in Japan. Most equipment made for America and Europe can't "see" channel 14 at all without using a modded driver or ROM, which means you'll also have to either do that or use Japanese hardware.

I did more research since starting this thread, and found the following articles.

Using WiFi Atheros chips in hamradio bands
Modifying Consumer Off the Shelf Wireless LAN devices for specialized amateur use

In simple terms, Wi-Fi uses the wireless band between 2400 and 2500 MHz. By compiling a driver that allows going below or above those frequencies for a chipset that supports it, you can have networks invisible to anyone else who hasn't done the same (i.e. virtually everyone). This is likely what the person I mentioned did.

Connecting to such a network from Windows clients would be impossible, but you can use the modded driver under Linux, or perhaps a DD-WRT router (where this is a paid feature called "superchannels") in client or bridged mode.