How is an IoT endpoint usually characterised, and what does each of those adjectives cost the designer?

"Smart, always-on, always-sensing, connected, secure, low-power-capable, small-form-factor devices at the edge of the cloud" — a list in which almost every item fights the others.

The description is worth unpacking because it is really a list of conflicting requirements:

• Smart — it does local processing rather than shipping every raw reading, which costs compute and memory.
• Always-on / always-sensing — it never gets the luxury of being switched off, so its idle draw dominates its battery life.
• Connected — it holds a radio link, and radio is typically the single most expensive thing it does in energy terms.
• Secure — it must do cryptography, which costs cycles and energy on a processor that has few of either.
• Low-power-capable — the budget that all of the above must fit inside.
• Small form factor — which caps the battery size, and therefore the budget itself.
• At the edge of the cloud — it is the outermost tier of a larger system, not a standalone product.

That is why IoT engineering reads as a permanent negotiation rather than a set of best practices: every desirable property is drawn from the same energy account. The recurring design move is balancing computation against communication — process locally and send less, or send more and process centrally — and picking whichever side is cheaper for the workload at hand.

Tip: when a requirement seems impossible on an IoT device, ask which of these adjectives it is competing with. The answer is nearly always "low-power".

Go deeper:

• Wikipedia — Wireless sensor network — states the constraint bluntly: energy is the scarcest resource of a sensor node, and it is what decides the network's lifetime.