Open sesame, CD-ROM!

The technique that allows you to do this relies on the mciSendString function from the Windows API. This function provides a general purpose interface to Windows' multimedia capabilities. This is its declaration:

Declare Function mciSendString Lib "winmm.dll" Alias "mciSendStringA" _
  (ByVal lpCommandString As String, ByVal lpReturnString As String, _
  ByVal uReturnLength As Long, ByVal hwndCallback As Long) As Long

Because the CD-ROM is considered to be a multimedia device, you can use this API function to control it. The first argument tells the device what you want to do. For example, pass the string "set CDAudio door open" to open the door, like this:

retval = mciSendString("set CDAudio door open", "", 0, 0)

You can see that the second through the fourth arguments aren't used in this case and are passed either a blank string or the value zero. Likewise, the function's return value can be ignored. Along with the function declaration shown above, you can put the following two procedures in a code module in your program to provide control of the CD-ROM door.

Public Sub OpenCDDoor()

Dim retval As Long

retval = mciSendString("set CDAudio door open", "", 0, 0)

End Sub
Public Sub CloseCDDoor()

Dim retval As Long

retval = mciSendString("set CDAudio door closed", "", 0, 0)

End Sub

Note that calling OpenCDDoor when the door is already open, or CloseCDDoor when it is closed, has no effect.