Small (touch-)screen areas on mobile devices often limit their capabilities for user interaction. In this paper we present GyroPen, a method that brings an experience similar to“drawing with a pen” to mobile devices without using a stylus and without the space restrictions typically imposed by a small form factor. The user can hold the mobile phone like a pen and “write” on any surface (Fig. 1). The trajectory of the phone’s “writing corner” is reconstructed from the phone’s sensors: its gyroscopes and accelerometers. Because the proposed method does not require to use a touchscreen, it is particularly appealing for small form factor devices or for devices lacking a screen.