Human interaction with wearable computers is an important research issue, especially when combined with mixed reality (MR) applications. Natural and non-obtrusive means of interaction calls for new devices, which should be simple to use. This paper considers the design of new interaction hardware, such as a wearable computer pen, a tilt pad, a wand, and a gesture pad designed using accelerometers for such scenarios. The very difficult problem of noise in small hardware accelerometers (in the form of random bias drifts), which seriously impedes it’s application in position measurement is also examined in detail. Kalman filtering has resulted in improved results, which are presented herewith. The application of accelerometers to design interfaces for use in mixed reality environments is also explained.