Tool to monitor wifi stability?

What i check first and foremost is interference with other neighbouring channels and routers tranmitting there and how it affects your signal strength...

So check Netstumbler or even better inSSIDer to perform your site survey at a first level of diagnostics...Own Android device? Check WiFi analyzer app...or http://www.androidzoom.com/android_applications/tools/meraki-wifi-stumbler_ixku.html

To dig event deeper you can turn to raw packet/wi-fi traffic capture tools and traffic analyzers (wireshark/ethereal, MS Network monitor to name a few).

Also worth mentioning for further troubleshooting is Xirrus Wi-Fi Inspector.

At a more practical level:

• avoid using microwave and Wi-fi at the same time
• avoid using 2.4 GHz cordless phones
• search for better antenna(s)
• reinstall or upgrade drivers
• install latest device firmware

Also, event logs are your friend...maybe setup a Snare syslog agent (http://www.intersectalliance.com/projects/BackLogNT/) and collect info across your hosts...That will definitely provide a wider perspective on what happens, the time it happens and help you see a pattern maybe repeating...