The PA-II and PA-II-SD both have WiFi capabilities and come with 2 laser counters. The difference is that the PA-II-SD comes with an internal microSD card reader and real time clock that logs the data and tracks time with or without a WiFi connection. Currently, you must remove the microSD card from the sensor and plug it into your computer to read and analyze the data. It is not possible to upload the SD card data to the PurpleAir map. The PA-II-SD is intended for places that do not have access to WiFi or have intermittent WiFi.