Okay so I'm new here and i love challenges, this project looks very interesting and you seem to have done your research on it. Now, I know I don't particularly have a Tensor Flow project to show you but this job actually doesn't require as much knowledge of Tensor Flow as you may think.
So the basic things we have to do actually don't require much experience with it.
I'll state the things which i'll have to do over here
1) Compile and install TensorFlow for your raspberry pi 3.
2) Compile and run the default camera recognition example.
3) Take the output of the recognition program and input(pipe) it into my program.
4) My program will basically read the output from the recognition program and search for the keywords(cellphone,smartphone,camera, or whatever else you may want to add.)
5) When it finds a keyword which has a high possibility to be correct, it will send 3 beeps to the speaker(You can provide the audio file) and then start recording for the time you mention and the location you specify and then resume the beeps as you said. or whatever else you may want to do.
I just have one question, how are you planning to turn off the beeps?
because in point 2. b) you said that "Sending signals to the speaker will resume after the video recording has ended."
Will it be like do 3 beeps before recording and some N number of beeps afterwards?
So the project is actually not as difficult as it may seem.
So that's all,
Cheers!
Arnav