During discussions in collocated work it is necessary to vote for results or to rate them to reach an agreement and continue working. To ensure impartiality and to avoid social embarrassment, the assessment should then be performed anonymously in so far as other groups members should not see directly how a person votes or rates. With a growing number of digital devices in collaboration, this requirement also concerns such kinds of equipment. Our approach of ensuring anonymity of individual votes and ratings submitted on personal mobile phones is to avoid shoulder surfing activities. For this purpose, we designed four device-based interactions that aim at being easy to use and eyes-free to perform to stay in touch with the environment and potential shoulder surfers. We conducted a user study to investigate these interaction techniques and observed seven groups with four participants each while testing the interactions. Participants evaluated usability and User Experience (UX) aspects as well as unobtrusiveness of the four device-based interactions. Furthermore, participants gave valuable user feedback and stated that our proposed interactions help to avoid shoulder surfing.