i remember that a years ago it was possible to detect silent sms on android phone with apps, i had it and tested it by sending a silent sms to myself, but if i' remember right then google modified the code to prevent apps from doing it.
Also someone asked for "credible information about threats posed by silent SMS." then here a video of an ex french DGSI (French Homeland Security) agent who explain that to track people location more accurately silent sms are sent to phone to force it to connect to the tower more frequently than usual.
https://youtu.be/mCwu8pTRYYY?t=1388 (enable english subtitles)
generated translation:
Then there is the active location. In this case, vraware forces an action on the mobile line via what is called a ping.
This is often called silent SMS. It is an invisible message for the user without notification or vibration that triggers a technical communication and this communication determines the activated cell and the location is immediately recorded.
And the investigator can set the frequency of his pings, for example 1 every 300 seconds or every 60 seconds for a tighter follow-up.
And the higher the frequency, the finer the accuracy, but the faster the phone battery drains.
But while he's usually right on his videos i think that his statement is wrong and based on old practices (when phones weren't keeping a constant connection to towers) and not factual anymore.