How are you planning to handle the user data though (who set what trigger when, etc.?) -- will you be selling it (even if anonymized) to third parties?
Cool! IB has an extensive API and they would be next on the list (hopefully Robinhood as well). At first it would not be automatic trading, but rather pull up an order form when the trigger fires. You can chose to set a market or limit order after the condition is met. Regarding selling the data, we have no plans to do sell it to third parties. If anything, we would like to offer insights back to the community of what we are seeing from the triggers, important levels and sell/buy interest.