Here's a source code release for .NET interop with Win32 features, including the Sensor API:

http://code.msdn.microsoft.com/WindowsAPICodePack

The Windows® API Code Pack for Microsoft® .NET Framework provides a source code library that can be used to access some new Windows 7 features (and some existing features of older versions of Windows operating system) from managed code. These Windows features are not available to developers today in the .NET Framework.