Active Level 10
Are you thinking about a ringtone that stand out against the background of a loco-engine and other industry noise? Even with the ringer set on maximum volume, we may tend, not to hear our phone ringing while walking on a busy street or riding a bike. Vibration may not be effective if the back case is hard or if the phone is not in the pocket.
I am just pointing the attention towards our most familiar and simplest beep-beep ringtones. I have been using beep-beep for a long time. No matter, whether the phone is in the bag, or in a closed room upstairs, my ears always picks it up against all noises. 
I think two important factors are there. 
1) Beeps are usually high pitched. 
2) Beeps are characterised by perfect silence between the signals, making it easy to detect.(unlike the smooth wave like tones which can never stand-out in a noise). 
I think the same factors are considered while choosing the name 'Bixby' also (BixBy).  Simply, easy to detect.
Beeps never annoy.