QR Droid  provides a free online QR code generator for nine different QR code types. One which I think is of particular use is the QR text generator. Simply type in your text, adjust the size and colour if your choose and the click generate QR code. Print the QR code and post it on the front door of your classroom. All parents/students need is a device with a QR code reader app (many of which are free) and they can scan the QR code and read your message. I also like the URL QR code generator which allows you to generate a code with a link to a website or YouTube clip.