I think you're overthinking it. Take your every day CSI episode; how many leaps of logic are made in a single episode so the good guys can catch the killer? Or almost any blockbuster action movie ever; how often does the villain make some obvious mistake allowing the good guys to take him out?
This is a staple of storytelling; sometimes the setting doesn't make a whole lot of sense if you think about it for even a second, but we let it go in most cases because otherwise the heroes would be dead in a ditch somewhere.
My advice; don't overthink it, and just go with the notion that there are flaws in Shadowrun security that can be exploited, because otherwise Shadowrunners wouldn't exist.
You can also try to explain it with simple cost effectiveness. Imagine a vast, complex system like that of DocWagon Seattle. They must have hundreds of thousands, if not millions of subscribers. Let's say that on average they get 100 calls a day, ranging from panic attacks to heart attacks in terms of severity. Now imagine if just 1% of those calls were false positives due to equipment malfunction (equivalent of a critical glitch for some reason) or wannabe hackers goofing around; that's 1 call they have to send a team to respond to every day, 365 days a year. The amount of resources they would have to devote to following up on dead ends (no pun intended) could quickly escalate beyond profitability.
Now add in the concept of noise; if a DocWagon contract holder finds himself in downtown Seattle or, god forbid, in the Redmond Barrens, on a particularly busy day, his wristband could easily be knocked out by a mere 3 noise. This is a situation I would expect to be nearly everpresent in a large sprawl, adding to the complexity of having to respond to a last known location if a wristband went offline. Similarly, if DocWagon were to respond every time symptoms like tachycardia (heart beating at more than 100 beats per minute) were to present itself, they would find themselves responding to a whole lot of training studios or gyms.
In short, I choose to think of DocWagon bands more as an active alarm system than a passive. DocWagon doesn't respond if the wristband shows normal readings associated with sleeping (or being knocked out by Narcoject), nor do they respond if the wristband goes offline because that likely happens to almost every subscriber at least once a day. Instead, they respond if the subject presses the button that specifically implies "Help! I'm in distress!". To my mind, this puts the DocWagon contracts more in line with the PANICBUTTON (TM) of old, which I personally think is fitting.