Meet SensorPush: a wireless thermometer and hygrometer that pairs with your iOS or Android smartphone to measure temperature and humidity in your home. It has a line of sight range of 325 feet. It pushes readings to your smart devices via Bluetooth. You get graphs on your phone to make sense of the data.
SensorPush simply lets you keep a closer eye on changes in your environment. It is available for under $50 at this time.