The Teensy Loader makes getting code into your Teensy easy. Just press and release the reboot button and the processor runs the HalfKay bootloader, which is automatically detected. Teensy Loader lets you download your code and reboot to it. Automatic mode downloads and reboots to your code the instant your computer detects HalfKay. The latest version of your code is always used. Just press the button and within 1 to 2 seconds your latest code is running!