Even more from the linked document:
System alignment beacons are on 406.022
First generation beacons were on 406.025MHz. That channel was open from 1982 to 01 January 2002. After then, no new beacons were built that used this channel only.
On 01 January 2000, 406.028 was added and assigned to new beacons through 01 January 2007.
On 01 January 2004, 406.037 was added and assigned to new beacons through 01 January 2012.
On 01 January 2010, 406.040 was added and is still being used for new beacons.
There are more channels set aside, but according to the document, they are either "reserved" or "available for future assignments/new developments". So, if you wanted to hear this stuff, you'd want to listen between 406.020 and 406.042MHz. You'd need something better than an FM capable scanner. You'd want something that could do AM/CW. They are low power (5 watts or so seems to be standard) and designed to be heard by overhead satellites, so you likely wouldn't hear one unless it was pretty close. The 121.5MHz homing signal, while still low power, would probably be easier to hear with an AM capable receiver that would cover that frequency. An air band receiver would work. There are often false alarms if you are around an airport or busy shipping port. They are pretty good about chasing those down since it can cause issues and increase the amount of time it would take a "real" activation to be received.
In the US, US Coast Guard and the US Air Force run the Rescue Coordination centers that handle these calls.
The future looks like the Medium Earth Orbit Satellites used by the US GPS, European Galileo, and Russian GLONASS navigation satellites will likely carry receivers for 406MHz beacons. This will improve coverage and result in nearly instantaneous notification of an activation. There are also plans to do a return message system using the Galileo satellites, so the RCC's could eventually send your EPRIB/PLB a message letting you know that your distress signal was received.
