Meet the Wimoto CLI001: a climate control sensor that can measure temperature, humidity, and light levels. It can measure temperature in Celsius and Fahrenheit, relative humidity %, and light level in lux. It sends the data to your iOS or Android devices via Bluetooth.
The device runs up to 3 years on a single battery. It acts as a data logger when your smart device is not around. In fact, it can record info for up to a month. Costs $49.