Reddit mentions of 130dB Personal Alarm Premium Emergency Safety Sound Whistle Self-Defense Security Alarm Cute Bag Decoration for Kids/Women/Girls/Elderly Self Protection (3 Pack, Black)

One option is something like the product in the youtube video below. There are versions on amazon in the $50 price range. Not the most aesthetically pleasing, but work well. Interior doors are generally flimsy compared to exterior doors so builders can save money. I would highly suggest "hardening" your strike plates which one of the videos below mentions. Low cost way is to get some longer screws which anchors it into the studs and not the pine frame. Another product are these 130db alarms. you just pull the pod and they off. Trust me 130 is MORE than enough for people to hear.

https://www.amazon.com/Personal-Emergency-Self-Defense-Decoration-Protection/dp/B077GNKC31/ref=sr_1_1?ie=UTF8&qid=1519288683&sr=8-1&keywords=rope+pull+alarm

https://www.youtube.com/watch?v=gM-VLZISzJw

edit
some basic videos on door re-inforcements.
https://www.youtube.com/watch?v=t7t2SiBp-G4
https://www.youtube.com/watch?v=5VdfW4eBfGA