A wireless drink container (102) can monitor a person's hydration and prompt him or her to drink more if appropriate. The drink containers as described herein can monitor liquid levels and communicate with external devices about the liquid levels and rate of consumption. One or more sensors (110, 130, 150) in the drink container monitor the liquid level within the container. A processor coupled to the sensor(s) estimates how much liquid has been removed from the container from changes in the liquid level and transmits a signal representing the change in liquid level to a smartphone or other external device. It also triggers an audio or visual indicator (154), such as an LED, that prompts the user to drink more based on the user's estimated liquid consumption and on the user's liquid consumption goals, which may be based on the user's physiology, activity level, and location.