At some point this morning (US Pacific time), perhaps around 1500 UTC, the notorious buzzer station on 4625.0 kHz broadcast two voice messages with the group military call sign MDZhB. At 1628 UTC, the transmitter is ominously silent, as heard here on WebSDR and by other people.
The text of these messages has not yet been reported. Presumably, it's in the usual Russian strategic format, which vaguely resembles the US "SKYKING" broadcasts in content and purpose.
This activity corresponds to a flurry of traffic on the Bear-H net, with markers and traffic on the summer ground frequency of 8895 kHz CW, and aircraft responding on summer frequency 9128 kHz CW. The aircraft transmissions were reported as unusually loud in the UK, and indeed some unusual RAF activity has been heard on the usual non-HF channels. There is no way to know whether this is related.
It is now 1640, and there is still no buzzer. Since Russian dead-hand nuclear missiles have not auto-launched, we can safely conclude (again) that the country's supposed fail-deadly system uses a different trigger. That is, if it really exists at all.