As the Internet becomes ever more accessible via smartphones, tablets, netbooks, and laptops, researchers have increasingly less control over how participants complete online surveys. Although options for online survey takers make these surveys more accessible than ever, researchers may not reap the benefits of increased accessibility if surveys are not configured to fit the wide range of devices available. Most current research on mode differences focuses on comparisons among paper, telephone, and online surveys, treating online surveys as a single mode. However, with so many devices available to access online surveys, researchers must consider the possibility that mode differences exist between devices within an online survey. This study examines respondent behaviors by device in a probability-based online advertising tracking survey over a one-year period. The survey contains open- and closed-form questions with a variety of response option scales. Paradata from the survey administrator provides the browser user-agent tag, used to determine type of survey-taking device, and time to complete at the item level. This paper will examine the effect of the device on survey taking behaviors such as item nonresponse, open-ended response length, and straightlining. Implications for future online survey research will be discussed as well.