The article by Dan Frommer features quotes from Lextech Labs CEO Alex Bratton that explain why the company decided on the $900 price point.
Frommer writes, “Why charge so much? Because for the people who are buying the app, it’s actually a relatively small cost. Bratton says his target customers are monitoring security systems for corporations, government organizations, universities, etc., that can run more than half a million dollars. For them, a $900 app is just part of the cost of doing business. Especially when the alternative — getting a custom piece of hardware developed, instead of using off-the-shelf iPhones and iPod touches — costs thousands per gadget.”

