Although it's not something new, network administrators are still facing old problems. One of these problems is to be able to detect rogue and/or fake access points in their networks and surroundings.The solutions available are mostly commercial and/ or proprietary, but still no open-source tool. Now there is: Beholder. The talk will include a brief introduction on the general state of the commercial WIDS and will be mostly focused on the Beholder project. Beholder is an C language opensource tool available (for now) for linux platforms, it can be used for whatever 802.11 technology the nic card supports and it isn't driver dependent, run in all available linux wifi driver.