The TECO institute is working on an enhancement for its project ProximityHat, an electronic travel aid (ETA). This paper is a state of the art analysis about new possible sensors for the ProximityHat. The following sensor types are being analyzed: laser range detection, ultrasonic range detecting, Doppler velocity measurement and image processing with a stereo camera. These sensors are used for gathering proximity and velocity data of external objects. Relevant works for each sensor type mounted on a mobile observer (human or robot) are discussed with a special focus on ETAs.