With three current SQL Server Compact versions (file formats) available
3.0/3.1 on Windows Mobile 6.x devices,
3.5 with Visual Studio 2008 and 2010,
and 4.0 currently available as a CTP (Community Technical Preview),
it can sometimes be hard to tell what the file version of a SQL Compact file in your possession is.
To help you, I have created a small utility that you can place on your desktop and drop any SQL Server Compact file on.
Place the SQL Compact Detector.exe on your desktop, and drop a SQL Server Compact file on it!