Measuring Wifi Strength on OS X

I’ve been setting up a wifi network in our new flat and have been looking for tools to help determine the best placement for the wifi base station. It turns out there’s a handy tool built right into OS X, which will tell you the signal strength being received by the Airport card for the network you are connected to. It’s hidden deep inside your library folder, and must be run from the terminal:

/System/Library/PrivateFrameworks/Apple80211.framework/Versions/Current/Resources/airport -I

It’s a private framework application, and while it’s in both Leopard and Snow Leopard, it may of course disappear in future. For now, however, it’s very useful. It’s especially good bed-fellows with the watch command, so you can see a continuously updated display as you walk around, MacBook in hand.

The number you’re looking for is the agrCtlRSSI number. I believe it varies between 0 and -100, with numbers closer to zero being better. For reference, my results are: standing right next to my Airport Extreme gives me around -34; performance is acceptable down to the -60 range; at -70 or below the connection starts to become problematic.

Unfortunately the optimum position is rather obtrusive, so more experimentation is in order.

Update: More description and other useful tools here.