I was disappointed to find that the improved Linux Kernel Orinoco drivers do not report power levels via the standardised iwconfig 'monitor mode'. When the iwpriv 'monitor' mode was available, Prism II packets were sent from the driver to userland. These packets contained extra information reported by the hardware, such as per-packet signal & noise levels. I think having SNR measurements is one of the most useful features of Kismet, as it allows to you roughly determine the direction to a network based on signal power. Therefore I took the old-style monitor mode code and transplanted it into the modern driver (in kernel version 18.104.22.168). Now both monitor modes are accessible. Kismet picks the older one (Prism II packets) first, before trying the standardised mode.
Without too much fuss, the Kismet SNR meter is back - for example:
The diff is attached below. Please be aware that it is not thoroughly tested and is supplied 'as is'! Also note the underscore in the file extension (for security reasons).