Determine Which Process is Reserving Serial Port

Updated Jan 28, 2023


Operating System

  • Windows

How do I figure out what process is using the COM port?

To find the process which is using the Serial (COM) Port, follow the steps below.
  1. Download the Process Explorer tool from Microsoft.
  2. Open Device Manager and expand Ports (COM & LPT). Right click on the target serial port and select Properties.

  1. Select the Details tab and change the value in the Property field to Service. Note the service value for searching in Process Explorer.
In the example below, COM port 11 is assigned to a USB-232. The COM port's service value is NiSerU.

  1. Open Process Explorer. You will see a screen similar to the image below.
  1. Select Find » Find Handle or DLL... in the menu.
  2. In the Handle or DLL substring field, type in the value that was obtained from Device Manager. In this example, we type in NiSerU
  3. Click Search and the results will populate to show which process is using a the particular handle.
In this example, the USB-232 shows as \Device\NiSerU1 being used by NIMax.exe