> The fair comparison would be intermittently transmitting a string of data versus intermittently operating a radio receiver, wouldn't it?
Good point. I don't know that this would actually work with BLE, as implemented on our pocket supercomputers (which I presume to be a useful part of the support system of a modern pacemaker).
But if we change the requirements to "Some kind of maybe not-even-invented-yet RF thing, maybe with a rechargeable translator device that a person keeps in their pocket to convert to BLE when that's useful" then: Sure. Intermittent receive could be used instead.
Whether that's more efficient or not is an interesting problem.
Transmitters tend to use more instantaneous power (ie, Watts) than receivers do, but a transmission can be very, very short. It doesn't care whether anything is listening or not. Transmitter wakes up, blurts out what it has to say, and goes back to sleep.
If a chunk of BLE data of this size takes 1ms of transmit time (it might), and it happens every 60 seconds (it might), then that's transmitting for 1.44 seconds per day.
So total consumed power over time (ie, Joules per day, or whatever) can be very low. That's part of how we got here -- BLE is built around this concept, and it all converges to make this easy to accomplish.
Meanwhile: An intermittent receiver tends to use less instantaneous power, but it usually needs to operate for a longer period. It wakes up and actively listens for instructions for a period of time. If none are received, then it goes back to sleep. Synchronizing free-running clocks is hard (and disciplining them is expensive, power-wise, compared to a sleep state), so maybe that receive window is 50ms every minute. Worst-case: The receiver operates for 72 seconds per day.
Even if receiving uses just 1/10th the instantaneous power as transmitting does (this is probably in the right ballpark), then the intermittent receiver still uses a ton more power over time -- especially if there are no transmissions to receive. (The receive window obviously closes if/when a transmission is received, so having something to hear can improve this some.)
But the end goal isn't just to wake the pacemaker up by pinging it. The end goal is for it to transmit data. So we still get to wake up the transmitter and have it do that.
Now, these are all made up numbers -- I think they're somewhere near reality, but maybe not. But it seems like kind of a double-whammy, to me, compared to intermittent transmit. :)