Both WiFi and Bluetooth are under the category of wireless. SensorPush sensors use Bluetooth, but a WiFi option can be easily added.
The sensors use Bluetooth LE to communicate, so on their own they are limited to Bluetooth range (e.g. around the house - like a Bluetooth speaker).
If you would like to monitor SensorPush sensors remotely (e.g. away from the house), you need to use them in conjunction with a SensorPush WiFi Gateway, which relays the data of any in-range SensorPush sensors to the internet using your local WiFi or Ethernet to your network.
The reason the sensors use Bluetooth LE to communicate is because it's more cost effective hardware than WiFi and it uses a great deal less power, so the batteries last a lot longer (in many cases 2 years) and the sample rate of the sensor can be a lot higher than if it used WiFi. A lot of sensors with on-board WiFi will sample once every 15 minutes instead of once per minute (like our SensorPush sensors), and their batteries die after a couple of months instead of a year or more -- which is a real annoyance when you're measuring hard-to-reach places like a crawlspace under a house.
So with a Gateway, you can not only add WiFi capability, but because of the lower cost sensor, you can have a larger array of energy efficient sensors pushing to the cloud for remote monitoring for a lot less cost. Plus, the SensorPush cloud service is included in the purchase price, so there's not monthly fee for the Gateway.
We may eventually move in the direction of wifi once it's possible to have more efficient systems.