I've been alive 64 years and and found that the best way is doing some noise when you suspect someone is near..
I use this technics at home and IT works...  

 Occupied! There you go. 

 
https://image.nostr.build/8e7f7fb641af8c61b58fc1d1e65edb213980b0f6d09485473965a259db88fc5d.jpg