The data is encrypted using two way TLS and the traffic is sent (without any processing or storing, or transmitting to third parties) to devices you have synchronized.
Your fear is probably not atypical, and as an indie dev it's maybe my biggest obstacle for this app's success. With that said, my number one priority for users is data security. I spent a great deal of time working on the security aspects alone, and if you have any questions about the details please feel free to contact me-- my information is available on the website linked.
EDIT: more clarity (I hope)
Can we remain sure that no data is sent otherwise?
As well: being able to launch a command on specific events would be nice for us hackers (if it's not already there, didn't check yet in depth).
EDIT: Also, raise your price!
Another question: Is it possible to run from cron? I don't want to have it running all the time. For example when run from the command line, is it armed by default or do I have to set it to arm manually from the menu?
If it's not armed when run, it would be nice to have:
OnCue --arm-video --arm-audio