Mark Hansen wrote:

Of course, during instrument training the instructor should take full
responsibility for see and avoid. However, during my training if the
CFII was unable to spot the conflicting aircraft and it was getting close,
I came out from under the hood and looked for it. IMHO, the safety of
the flight was far more important than staying under the hood and not
helping.

Besides the risk of injury or death, you're also PIC.

Usually, I spotted it within a few seconds and just went back under
the hood.

I wouldn't care for any system that prevented me from being able to
do that.

Same here, and I've only had to help twice, but I'm glad we don't have
to completely block the left front corner of the cockpit.

On a side note, the CRM method I set it up with safety pilots and
instructors, as well as suggest when I'm acting as safety pilot, is that
the person looking will also answer the ATC traffic calls themselves.
The flying pilot will still do all the normal IFR radio stuff, but this
simplifies internal cockpit comms.