Most connected devices are retired not because they break but because they stop receiving software updates. The support window is therefore the number that determines what a purchase is worth over time.
Updates carry security as well as features
A device connected to a network runs software that will eventually be found to contain flaws. Patches close those flaws as they are discovered.
When patching ends, known weaknesses stay open permanently, and the device becomes progressively less safe to keep on a home network.
This applies well beyond phones and computers. Televisions, cameras, routers and appliances all run software subject to the same problem.
Cloud dependence turns support into function
Many products rely on a manufacturer's servers for core features, sometimes including basic setup and control.
If that service is withdrawn, the hardware may lose functions it was sold with, even though every physical component still works perfectly.
The degree of dependence varies enormously between products in the same category, and it is rarely stated on the box.
Support length is a business decision
Maintaining software for an old model costs engineering time that generates no new revenue, so support periods reflect commercial priorities rather than technical limits.
Premium ranges typically receive longer support than budget ranges from the same manufacturer, which is part of what the higher price buys.
Some manufacturers now publish a minimum support duration. Where they do, it can be compared directly and is one of the few honest long-term specifications available.
The clock usually starts at launch
Support is commonly counted from the model's release rather than from your purchase, so a heavily discounted older model may have consumed much of its window already.
A clearance price on a device two or three years into its life can therefore represent less value than it appears.
Checking the original release date alongside the stated support period converts the discount into a cost per remaining supported year, which is the comparable figure.
Longevity is a specification worth weighing
Between two similar products, a longer support commitment is often worth more than a modest hardware advantage, because it extends the period over which the purchase is useful.
Independent alternative software exists for some device types and can extend life beyond official support, though it demands technical confidence and voids warranties.
For most buyers the simpler approach is to treat the published support window as part of the price comparison, in the same way a warranty length already is.