Is there an API call to start a scan for hardware devices

Related to Programmatically uninstall a device in windows device manager

My answer from there:

To force the 'scan for hardware changes' checkout "How To Force Reenumeration of a Device Tree From an Application" the sample there shows how to force the entire tree to be re-enumerated.

Not sure if this will help your overall problem but this should answer the question in your first sentence.

I originally did something like this using Nullsoft's NSIS installer a few years ago.

If you just want to trigger a vanilla hardware scan you can use the following code (provided in C# per the .net tag in this question):

This is the wrapper class for the P/Invoke functions

public static class Win32Api
{
    public const int CM_LOCATE_DEVNODE_NORMAL = 0x00000000;
    public const int CM_REENUMERATE_NORMAL = 0x00000000;
    public const int CR_SUCCESS = 0x00000000;

    [DllImport("CfgMgr32.dll", SetLastError=true)]
    public static extern int CM_Locate_DevNodeA(ref int pdnDevInst, string pDeviceID, int ulFlags);

    [DllImport("CfgMgr32.dll", SetLastError=true)]
    public static extern int CM_Reenumerate_DevNode(int dnDevInst, int ulFlags);
}

This is a sample of how to use them

int pdnDevInst = 0;

        if (Win32Api.CM_Locate_DevNodeA(ref pdnDevInst, null, Win32Api.CM_LOCATE_DEVNODE_NORMAL) != Win32Api.CR_SUCCESS)
            throw new Exception("something...");

        if (Win32Api.CM_Reenumerate_DevNode(pdnDevInst, Win32Api.CM_REENUMERATE_NORMAL) != Win32Api.CR_SUCCESS)
            throw new Exception("something else...");

I just quickly translated this from the MSDN C++ docs and tested it in a spike so I know it works but it's not production quality. Also, if you care about the specific return codes you can look them up in cfgmgr32.h.

Does my answer at the following help? How can I find out a COM port number of a bluetooth device in c#?

In brief use System.IO.Ports.SerialPort.GetPortNames() or WMI to list the serial ports, e.g. PowerShell command:

C:\> Get-WmiObject -query "select DeviceID,PNPDeviceID from Win32_SerialPort" 

Which can also be done in code.