[Johnythree]

> antenna is tuned to the maximum allowed emission power per local regulations

Actually it's not. The antenna is tuned to give a peak in output. It's either correctly tuned, or it's off tune.

It's the design of the whole transmitter/battery/antenna which chosen to give a compromise between battery life and max allowed output.

Few transmitters will come close to the max legal power, and if they did, de-tuning the antenna would result in a very inefficient compromise.

If you include a (dummy) human in the test environment you will (with luck) be close to optimum. By not including a human, you can be sure that the results will be worse in actual use.

[wallaBBB]

Not sure what products your experience comes from, but I am talking explicitly about keyfobs. This is generally produced by Tier 1 suppliers, not the OEMs themselves, and not too many players in the field. With the MCU suppliers it shrinks even more (talking about handsfree models, most common in the market, utilizing LF for localization and standard RF bands for Tx).

MCUs are highly specialized (also not publicly available), and you can play with the tuning registers up to several digits without much performance loss. 3xx/4xx MHz ones you can easily go over the regulation limits (IIRC in JPN occupancy is taken together with the power into the calculations, it's a very crowded spectrum...).

If a spread spectrum is used at 8xx/9xx range, there there is no worry of hitting the limit, here usually battery life and max peak current are limiting, and fine tuning is often done for individual samples at EOL in the plant. It doesn't necessarily mean that all at 8xx/9xx are spread spectrum, but the "premium" (usually half-duplex) are. They provide a lot better performances at low SNR (and thus great range) compared to the standard FSK/Manchester 1 or 2 CH fobs.