A very simple weather station based on ESP8266.
Made to protect crops from frost and take a cost arround 10€. It's designed to connect to a WiFi connection and send sensor measures to dedicated ThingSpeak server. ThingSpeak is an free IoT platform. Then, you can connect your mobile with the server through differents free apps available in Google Play. You only need to create a server in this platform and introduce API Key in the code of ESP8266.
Also you can add more sensor to your ESP8266 and, adding a few lines to the code, make more measures of your environment.