These are so nice and loud! They don't alert anyone but are loud enough to scare someone. It helped me feel so much more secure in my apartment.
Drop a dowel rod in the back of the track to keep the door from sliding open. Those doors can be lifted from up from the track and pushed in but that’s pretty hard to do, especially if the door is a tight fit for the track. I don’t know if any way to prevent lifting and pushing in, but you can get security seals that will set off an alarm if broken (like this). The alarm won’t go anywhere like the police or a monitoring company, but the noise should scare someone off. Then put one of those “protected by ADT” or whatever stickers up.
It won't necessarily stop entry but get a door wedge with an [alarm](3-pack upgraded door stop alarm -great for traveling security door stopper doorstop safety tools for home set of 3 https://www.amazon.com/dp/B06XVQN9W2/ref=cm_sw_r_cp_apa_i_gTl-Eb85JDQGH). They're pretty loud when they go off and would let know if your door is opened while you're in the bathroom or asleep.
Also, I don't know if it got mentioned but get locks for your windows. They also sell [alarms](ge personal security window/door, 4-pack, diy protection, burglar alert, wireless, chime/alarm, easy installation, ideal for home, garage, apartment, dorm, rv and office, 45174, 4 pack https://www.amazon.com/dp/B00FGPM1SS/ref=cm_sw_r_cp_apa_i_4Vl-EbXQQH7X1) that are made of two parts that go off when separated, so you put one on the window frame and one in the window itself, if someone opens/closes the window you will know.