Murders are detectable outside of homes. Is someone missing? Yes? Then start an investigation.
They could be missing already, or be unregistered kids, or recently arrived unregistered migrants. Not everyone who is murdered is noticed missing. Also, very few of the people who are missing have been murdered.
So what do you propose we do, regularly search all houses looking for bodies? These hypotheticals are edge cases which we already accept will in practice go unpunished. To eliminate them would involve violating the 4th amendment.
No, just arguing against your suggestion that they are not crimes if they are not detected by straightforward means.
If someone detects a murder by extremely technological means, say while using muons from cosmic rays to image though a structure like they are doing at Fukashima at the moment http://prl.aps.org/abstract/PRL/v109/i15/e152501, then that murder is still a crime whatever the method of detection.
Now it is reasonable to argue that growing weed should not be a crime in the first place, but to argue that growing it indoors should not be a crime on the basis of the level of technology required to detect it, does not seem to make any sort of sense.
So long as that somebody is not the police actively looking for a crime without a warrant, then that should not violate the 4th amendment.
I feel that I should emphasis that I am not proposing a change to existing law. I am merely advocating the point of view that new fancy technologies should, by default, be considered unreasonable searches.
They could be missing already, or be unregistered kids, or recently arrived unregistered migrants. Not everyone who is murdered is noticed missing. Also, very few of the people who are missing have been murdered.