I read a couple of things at Nordic but I concluded that this is too advanced for me right now. I only started with an Arduino starter kit a bit more than a month ago and still lack the level of knowledge about what is going on “behind the scenes” to make sense of what I read there. Until I feel confident that there is a good chance of success making this work, I will use the system ON sleep! This gives me 22 µA while waiting and about 130µA for a second when advertising at the push of a button. That gives me about a year from a CR2032. Crazy! I may even add deep sleep after an inactivity period and use an initial button press as an on-switch and it will last years.
On the scanning end, I have deep sleep with ADXL345 wakeup (and a 18650 battery so power is not really a huge concern). This has become obselete because my ADXL345 board needs 60µA, so I would be better off with system ON sleep. At least I learned something while developing it!
About the BLE, the beacon worked in testing. I can revisit more elaborate communication if I turns out to be unreliable in practice. I already have done it before using notify in code that I derived from the custom_hrm example. I will revisit that if I am not satisfied with the performance regarding a quick succession of button events. But first, onto the next problem. I have two buttons working, but I might like to have three and there’s only two straightforward interrupt pins. After this I draw a line! 