By studying a basic cloud based IoT end-to-end implementation, you can (with some determination) build your own IoT platform that could scale from supporting many hundreds of IoT client devices to many millions.
The basic implementation in question uses R3 Arduinos as client devices (with serial GPS and WiFi) that submit data via a web API to cloud based storage. A cloud hosted web UI visualizes the data using Bing Maps and D3 charts:
All source code is available for download and running on Arduinos and local PC: Build Your Own IoT Platform
Client devices are not limited to Arduino; any internet enable device that can be programmed to perform HTTP post should work. Determined coders should be able to implement their own monitoring and alerting mechanisms, if necessary.
Thanks
Kashif