Multiple accounts per household are allowed but in order to avoid duplicate participants in a study, we have a mechanism in place that allows only one person per household to take part in a particular study.
Please keep in mind that a household is anyone sharing an IP address with you. This is at home, your workplace, school, etc.
Here is an example:
If person A and B are from the same household and person A participates in Study X then person B will automatically be ineligible for Study X. Person B will only be eligible for studies that person A has not completed and vice versa.