Has anybody ever had any experience with installing an alarm or any other anti-theft device? prices? where to get them?

what is it for ? ebike?

I mean one fr the apartment!

I used to sell burglar alarms. I had this sales pitch I'd use with the ladies. All I had to do was say 'You need an alarm' - At 3 in the morning, sitting on the bottom of her bed.

Thanks for the troll reply, Napoleon.

I was a security specialist before coming to China. Since here I've installed several systems. I can tell you very clear.....
DO NOT BUY, USE, INSTALL ANY PRODUCT FROM CHINA! You are throwing away your money. They are all total crap and if lucky may work 6 months at best.
Buy outside China (Ademco, Elk, DSC) and install yourself. Do not let anyone in China do it. They are very bad and will not install correctly. JM2C
You can use door/window contacts from China. As far as Smokes & PIR's ok IF you know which ones to buy.

Xiaomi has recently started to sell a system, looks interesting