ZeroTrace Companion
Serial Ports
What a COM port is, where to find one on each operating system, and the permissions Companion needs.
A serial port (also called a COM port on Windows) is a virtual interface your operating system creates when a USB device announces itself as a CDC ACM device. ZeroTrace devices use this standard so they appear automatically — no special install required, in most cases.
How to see what serial ports your OS exposes
# PowerShell
Get-WMIObject Win32_SerialPort | Select-Object Name, DeviceID, Description
Or open Device Manager → Ports (COM & LPT). Plugged-in devices appear as USB Serial Device (COMx) or with the chipset vendor's name.
Permissions
Companion needs read/write access to the serial port to talk to the device.
Windows
No special permission required for standard CDC devices. If your device uses a CP210x or CH340 chipset, you may need to install the chipset's driver from the vendor's website.
macOS
No special permission required. macOS may show a one-time "App is requesting access to your USB devices" prompt — allow it.
Linux
By default, only the root user and members of the dialout group can read serial ports. To grant your user access:
sudo usermod -aG dialout $USER
Log out and log back in for the group membership to take effect. Verify with:
groups | grep dialout
If the group is uucp instead (some distributions), use that group name instead.
Running Companion as root (via sudo) works but is not recommended. Add your user to the right group and run Companion normally — it's the standard approach and avoids the security risks of running a GUI app as root.
Why your device might not appear
Common causes, in rough order of likelihood:
| Cause | Fix |
|---|---|
| Charge-only USB cable | Replace with a data cable. The cable that came with your device is fine. |
| Device not powered | Check the device's power LED. Unplug, wait 5 seconds, replug. |
| USB hub issues | Connect directly to a USB port on the computer. |
| Driver missing (Windows / older macOS) | Install the chipset driver — usually CP210x (Silicon Labs) or CH340 (WCH). |
| Permission denied (Linux) | Add user to dialout group; log out and back in. |
| Port already open | Another application has the port — close it (or use Companion's port picker, which marks busy ports). |
| Firmware crashed | Hard-reset the device by holding the reset button for 10 seconds. |
If your device appears in your OS's device list but Companion does not detect it, see auto-detection — Companion may have probed the port and decided it does not match a known device signature.
The baud rate question
Different ZeroTrace device types run at different baud rates:
| Device | Baud rate |
|---|---|
| ZeroTrace HID | 115,200 |
| ZeroTrace BLE Logger | 115,200 |
| ZeroTrace AirLeak | 921,600 (high speed for live wireless data) |
| Custom firmware | User-configurable |
Companion picks the right baud rate automatically when it identifies the device during the auto-detection probe. You normally never have to think about this — but it matters when you're using a generic serial terminal to talk to the same device, or when you're configuring custom firmware.
How Companion behaves with the port
A few invariants worth knowing:
- Single-owner. Only one application can open a serial port at a time. If Companion has it open, your generic terminal cannot — and vice versa.
- Non-destructive. Disconnecting a port in Companion releases it cleanly. Other applications can use it immediately afterward.
- Auto-recovers. If the device is yanked mid-session, Companion handles the broken pipe gracefully and offers to reconnect.
- Survives restart. Settings remember the last-connected port; auto-reconnect (off by default) re-attaches at launch.
Multiple devices on one machine
Yes — see multiple devices.