Project: Trash Can, Sound Sensors, and Security Doll

Hello there. I have 2 years of experience in Arduino, and this is my first time creating such a big project for our research. Our teacher recommended us 2 different robot researches to make.

  1. Trash Can that can open lid when it hears a clap (using sound sensor) and also obstacle avoiding
  2. A "Security Doll" that automatically shouts/moves when it hears burglar sounds.

Questions:
a. Which one is easy to do in terms of time and work, and relevant to human needs? (of course, what I am doing is a research project. And I am not the only one making this: we're 5 in the group)
b. Which one is more expensive (in this type of research, money is the key to success)
c. Overall, which one is better to make?

I hope someone would help me ASAP. Thank you very much.

I would think it easier to detect a clap than "burglar sounds".