Ekahau HeatMapper is a free software tool for quick and easy coverage mapping of Wi-Fi (802.11) networks. It’s the only free, easy-to-use tool that shows, on a map, the wireless network coverage in your home or small office. HeatMapper also locates all access points. HeatMapper also provides a real-time view to all access points and their configurations.
HeatMapper uses your built-in wireless network adapter, therefore, all you need is a Windows-based laptop with wireless. And it takes just one minute to install.