That's a BIG pretty chunk-o-chert!  Thanks for the pictures!
The yellow end is closer to the natural color of the chert down there, but yellower. And the color on the red end looks like it's through and through the rock and not just surface color. The whole piece looks more agate-like than a lot of the chert down there, but I would still call it chert.
You'd need someone with a mighty big saw to cut a few slabs off that chunk but it would be very nice to see. Good looking rock!

Well, yes, the red and yellow colors are caused by Hematite and Iron Oxides, so I would imagine that's what's setting off your metal detector.
Iron-bearing minerals within most "hot rocks" will cause a metal detector to go off. These iron bearing minerals are predominately the iron oxides: magnetite, hematite, limonite, maghemite and lepidocrocite.

And you can try and ask at some of the countertop places about cutting but I doubt they will be able to. Most of their saws and equipment are geared toward cutting the large flat slabs of rock they get. I doubt they would even have a saw that could cut this monster. You'll need to find somebody with a lapidary slab saw and it would probably have to be atleast a 24" saw. Also, and I hate to say this, but if you really want to get it cut, it would most likely have to broken into smaller pieces to get in the saw. So, you might want to leave it whole. It's been doing a good job on the porch for the last 10 years as it is!

Agreed! It was doing a fine job right where it was at! 

But yes, checking those natural holes, sometimes called "vugs", are what you want to do. Those "drusy" crystals are a good sign. That may be all there is in that outcrop, but it's a sign there could be more bigger and better. Some of that drusy is very pretty, too.