Autonomous AI agents, now embedded in everyday browsers, can complete online surveys and experiments with the click of a button, threatening the integrity of behavioral research that depends on online samples. Existing defenses, such as CAPTCHAs and attention checks, are easily bypassed. Webcam eye tracking offers a different defense: proof by presence. Unlike behavioral signals that AI agents increasingly mimic, gaze relies on physiological signals that are not feasible to counterfeit. We introduce a compendium of open-source tools that integrate webcam eye tracking into the platforms responsible for most online behavioral research: Qualtrics for surveys; jsPsych and PsychoPy for cognitive experiments; and oTree for experimental economics. We also provide guidance for researchers to screen out AI agents without penalizing human participants.