I'm sorry Sanddancer, but your skillset has gone obsolete.
Keys, along with such ancient crafts as customer service, and the village simpleton, bobbies uniforms, & boy scouts in shorts, have now been superceded by arcane new technologies such as 'BioMetrics', and 'Building Management Services'.
I'ts join the dole queue mate, or go to some obscure college and get an 'ology.
If the keys are on rings you could possibly hold hundreds if not thousands of keys depending of the design and weight of the keys !!
I suggest a bit of finger weight lifting exercises for such an eventuality !
I cannot post the "Finger" exercises on this site but I am sure most of the members on this site with have seen them before and are well versed in the practice of "Fingering" !
The only keys I hold are for the house. When I go out and get 'locked' I always make sure I have the keys to get in. In Ireland we are still using wheelbarrows for key holding. We are becoming more advanced, slowly but surely. How do you recognise a keyholder in Ireland? He/She is the one pushing the wheelbarrow.
Well that is good if you have neighbours you can trust and are always in, but many people won't. I leave mine with relatives, close enough for me but I wouldn't like the ambulance to have to go round there if I needed one. Also security people often advise having other locks such as bars that can only lock and unlock from the inside, they never seem to think about how people will get in if there's an emergency.
Stick to what you know mate as you clearly have no knowledge on biometrics systems and their advantages.
'Fingers tend to go off'?? I wouldn't bother commenting on things you have no knowledge unless you know what you're talking about. You only jumped on this as I had commented. You're a bit of a troll pal.