Hello,
I understand having concerns about safety. Even though we call the PurpeAir network a hotspot, it does not provide access to the internet. If a device were to connect to the PurpleAir network, it would disconnect from the internet and only have access to the sensor’s Wi-Fi settings. Additionally, once the sensor is configured to Wi-Fi, you should no longer see it as an available network. Therefore, it removes it as an option for surrounding networks to connect to.
You can find more information about security here: PurpleAir Sensors Functional Overview