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Wi-Fi signal detectors should let you track down a wireless signal before booting up your notebook and wasting power. Unfortunately, early versions of the devices didn't work very well. I tested three new devices and found them dramatically more useful than previous products.

Kensington's $30 WiFi Finder Plus is about the size of a Tic Tac mints box. To use it, simply press a button; if the device locates an 802.11b or g wireless signal, it indicates the strength by lighting from one to five green LEDs. A single blue LED lights in the presence of a Bluetooth signal. The device seemed quite accurate, but with each click it latches on to a single signal, so expect to push the button repeatedly to find the strongest signal.

Smith Micro's $30 QuickLink Mobile Wi-Fi Seeker is even littler than the Kensington unit and has a single button. Hold down the button, and while you walk around, the device will display the ever-changing signal strength of detected 802.11b and g networks in the area, via four red LEDs.

Canary's Digital Hotspotter sells for $50. Bulkier than the other two devices but still easy to pocket, the Digital Hotspotter not only notes 802.11b and g signal strength but also reports the name of the network (SSID), its broadcast channel, and whether the network is encrypted or open.

If you just want to know if a signal exists and how strong it is, either the Kensington or the Smith Micro device will do the trick; if you're interested in finding out more detailed information before you break out your notebook, pay extra for the Canary.