From coins and brooches to medieval belts, his finds have made their way into museum exhibitions up and down the country.
And the thrill the 61-year-old, from Cottingley, gets every time he discovers a new item spurs him to keep going and uncover more of the region's treasures.
"It's a great buzz knowing that someone has dropped this item years ago, and probably got back home and panicked that it was gone," he said. "It's some feeling knowing you are the first person to see or handle it for hundreds or thousands of years."
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Mr Smith, a chef by trade, began his hobby in the 1990s.
His detecting equipment, worth around Â£1,400, helps filter out valuable or historical objects hidden underground.
But deciding where to search can be challenging.
"You go on names," he said. "For example if a place ends in a Y like Selby or Wetherby, then there's likely to be something Viking related there.
"We also look at the land, and look what is nearby, if there's any historical churches. A land pattern of ridges and furrows normally dates back to Saxon times.
"These things give us a clue there might be something there worth uncovering.
"We then approach the land owner for permission and begin the search."
Mr Smith's finds include a Viking Thor's hammer, a 15th century medieval belt mount with a Tudor rose, and a King Edward III gold coin.
"I remember when I found that [the latter coin], I had found nothing all day," he said.
"Some of the lads I was with were taking the mick.
"And then right at the end of the day, I got a signal and I found half a Roman ring in this hole.
"I just happened to glance at the hole again and there was a medieval gold coin in there so I was dancing about a bit in celebration."
Mr Smith often turns to forums and Facebook groups for advice on what he has found.
He then declares any items with gold and silver, believed to be more than 300-years-old, to the Portable Antiquities Scheme, a requirement under the 1996 Treasure Act.
Today (August 18), an inquest at Wakefield Coroner's Court was held to determine whether one of his most recent finds was treasure.
He unearthed the medieval silver gilt ICH badge while searching a ploughed field in Adel, Leeds on October 27 last year.
The court was told it dated back to the 1300 to 1500 period and included a christogram in gothic lettering meaning Jesus the Saviour of Man. The inscription featured on many dress accessories during that period.
Coroner David Hinchliff said: "It contains a minimum of ten per cent precious metal and it therefore qualifies as treasure."
Speaking afterwards, Mr Smith said he had an inkling it would be treasure. "When I found it I said 'I hope this is what I think it is' - and it was," he said.
The badge will now be valued and Mr Smith could receive a reward.
A museum may want to take the treasure, but if not, it will be returned to him - and added to the collection of historic coins and fashion accessories he has been able to keep over the years.
"Metal detecting is one of those hobbies that has you hooked", he said. "You never know what your next signal is going to be, if it's rubbish or one of those 'wahoo' moments.
"It's very addictive, you just want to get out all the time.
"If it wasn't for the metal detectorists half the museums would be empty. Our finds can end up being another piece of history for people to look at.
"We are helping archaeologists too as we do come across whole historic sites and settlements.
"It makes you wonder what else is still out there."