By using a open source program named Hotkey (from , a keyboard with an interface that is available on your computer and the Web services of a simple interface can be built to generate alert messages. The combination makes a very low cost and simple to implement system for creating sensor inputs on your home computer. The software is free, the web service can be free depending on service required, and a low cost keyboards (perhaps you have a old keyboard gathering dust). With these three pieces the computer side of a home monitoring system can be implemented. Keyboards work on a simple concept, the closing of a connection on a grid is decoded into a number that represents the key or key’s depressed. So if one’s sensor could push buttons on a keyboards it could generate all the information needed to send a alert. The complexity of both pushing a button, and then a number keys in sequence is not a simple interface. Modifying a keyboard to allow for electrical closure of the key pads is a mater of opening up the keyboard and choosing the key or key’s you want to activate and making a wire connection. Nicely, Windows supports having more then one keyboard attached to your computer at a time, so you can modify a keyboard for use as a sensor input and still have your favorite keyboard to use. This keyboard has three layers of material making up the key array. Two contain the signal, a spacer layer is inserted between creating an air gap. Pushing on the key presses the two signal layers together completing the circuit. Once the circuit is closed the electronics of the keyboard convert that closure into a message to the computer. The keyboard array is made of two or more arrays that use the closure of a connection point in that array to determine which key was depressed. The choice of keys to use in making your sensor is up to the user, however keep in mind that if your system is to be used with an unmodified keyboard as well some care is needed in picking those keys. I suggest combining Ctrl, Alt, or the windows key, these can be hardwired closed, and the keyboard then generates code based on that combination. Once you have opened up the keyboard you will discover that the electronics portion is very small ( 1,25 inches by 3 inches for example). So we made a small box that contains the electronics from the keyboard and bring the connections to the barrier strip. The windows key is permanently closed, closing the connections on the barrier strip generates the keystroke as “windows key” – x, c, v. Using Hotkey’s ability to create custom key sequences and automate events from single Keys, we convert these key closures into a simple interface to generate sensor message to’s web services. Hotkey is a windows utility with numerous features, however for this application we use very little of Hotkey’s abilities. By adding to Hotkey’s INI file and auto loading Hotkey keyboard closures generate request to our server. The request are converted into alerts that can then be sent via email or voice to your Cell phone, office email, phone list. (all service require registration, some service have fee’s, detail at My other articles on creating simple sensors here at can be applied, you need a switch or relay closure. The signal in the keyboard can not have any external voltage applied! We can have more then multiply closures as most keyboards report the last key pressed even if other keys are stuck. For more information and to register please visit