# A Serial Monitor for macOS > macOS ships no graphical serial monitor. Here is how to find your device under /dev/cu, why screen and cu are awkward, and a better native option. > > macOS · June 29, 2026 · by Alex Spataru · https://serial-studio.com/blog/serial-monitor-macos On Windows, when you need to look at a serial port you reach for PuTTY, RealTerm, or the vendor's tool. On macOS there is no equivalent that ships with the system. You get two command-line utilities, `screen` and `cu`, and that is the whole toolbox. For a lot of people this is the first surprise after switching to a Mac for embedded work. This post covers how to find and open a serial device on macOS with what you already have, why those tools get frustrating quickly, and what to use instead. ## Finding the device Plug in your board or adapter and list the serial devices: ```bash ls /dev/cu.* ``` You will see something like `/dev/cu.usbserial-1420` for an FTDI or CP210x adapter, or `/dev/cu.usbmodem14201` for a board with native USB such as a Uno R4 or a Teensy. You may notice each adapter also has a `/dev/tty.*` twin. The difference is real and worth knowing. The `tty.*` device waits for a hardware carrier-detect signal before it opens, which is a leftover from the modem era and usually causes a program to hang. The `cu.*` device (short for "call-up") opens immediately. For talking to a microcontroller, always use `cu.*`. Serial Studio only lists the `cu.*` devices for exactly this reason. ## Using screen, and why it grates The quickest look is `screen`, giving it the device and the baud rate: ```bash screen /dev/cu.usbserial-1420 115200 ``` Text starts scrolling. That is about as far as the good news goes: - There is **no scrollback**. Whatever left the top of the window is gone. - There are **no timestamps** and no way to plot anything. You are reading raw text. - **Exiting is cryptic.** You press `Ctrl-A`, then `K`, then confirm with `y`. Nobody guesses that the first time. - If you close the terminal window without exiting cleanly, the session **stays attached in the background** and holds a lock on the port. The next time you connect you get "Resource busy" and have to hunt down the stray `screen` process. `cu` is the other built-in. It has its own lock-file quirks and the same fundamental limits: it is a text pipe, not an instrument. ## A note on drivers Recent versions of macOS include drivers for the common FTDI and CP210x chips, so those adapters usually appear under `/dev/cu.*` with no extra install. The cheaper CH340 and CH341 clones sometimes still need a driver. If `ls /dev/cu.*` does not show your adapter after plugging it in, an outdated or missing CH340 driver is the usual cause. ## A native app that does the rest Serial Studio is a native macOS application (a universal build for both Apple Silicon and Intel), and it fills the gap those command-line tools leave. It lists the `cu.*` devices in a dropdown, so there is no path to type. The console gives you proper scrollback and a hex view for binary data. And because it is built for telemetry, it does the thing `screen` never will: if your device streams numbers, Quick Plot draws them as live graphs, and you can export the session to CSV. You do not have to give up the terminal. `screen` is fine for a five-second sanity check. But when you actually want to *read* the data, watch it move, and keep a record of it, a real graphical monitor is the difference between squinting at scrolling text and seeing what your device is doing. If you are new to serial ports in general, the companion post [How to Read Data From a Serial Port](https://serial-studio.com/blog/how-to-read-a-serial-port) covers baud rates and framing before you connect. ## Frequently asked questions ### How do I exit screen? Press `Ctrl-A`, then `K`, then answer `y`. That kills the session and releases the port. Do not use `Ctrl-A d`, which *detaches* instead: the session keeps running in the background and keeps the port locked. ### Why does macOS say "Resource busy" when I open the port? A detached or orphaned `screen` session is still holding it. Run `screen -ls` to list sessions and `screen -X -S kill` to end one, or find the process with `lsof /dev/cu.*` and quit it. The port frees immediately; you do not need to unplug anything. ### My board doesn't show up under /dev/cu.* at all. Now what? Three causes cover almost every case. The cable is charge-only (surprisingly common; swap it for a known data cable). The adapter uses a CH340 chip and needs its driver installed. Or the board itself is not enumerating, which you can confirm in **System Information → USB**: if it is not in that list, no driver will help, and the problem is upstream of macOS. ### Does the Arduino IDE's serial monitor work on a Mac? Yes. If you already have the IDE installed, its Serial Monitor and Serial Plotter work the same on macOS as anywhere else, and they are fine for quick text output. The limits show up when you need scrollback, timestamps, logging to a file, or more than a basic plot, which is the gap the tools in this post fill.