In the past couple of years many companies have started offering "smart home", "market-ready, connected devices" as an "Internet of Things". These are relatively inexpensive, easy-to-install, smart phone oriented devices for use in the home to monitor temperature, humidity, energy and water use, doors, motion and control things like lights, pumps, outlets, appliances, etc. Few of them are farm oriented but for a basic monitoring system they may be adequate. Below are some I have researched but not yet tested.
SmartThings, (www.smartthings.com), San Jose, CA
In Aug, 2014, this company was bought by Samsung to become part of its Samsung’s Open Innovation Center group but claims it main its philosophy of being a "totally open smart home platform that brings together third-party developers, device makers, and consumers." Can handle a wide variety of sensors. Reviews indicate user interface is rather clunky at the moment.
Smartenit (formerly SimpleHomeNet), (www.smartenit.com), San Juan Capistrano, CA
Provides two gateway options ($160 - $200), repeater ($60) and about 50 different sensors and control units. Temp/Humidity is $70; solar radiation sheield is $50. ZigBee, Insteon and WiFi protocols used. No information on radio ranges on website. Fairly good website but some details missing. Pros: Wide range of devices available to control appliances, lighting, pumps, etc; asy installation; good smartphone software with ability to set triggers to control devices. Cons: no temperature probe option, no radio range info on website, no other ag oriented sensors, no weather stations.
CAO Gadgets Ltd (http://wirelesstag.net), Irvine, CA