Gas Leak - Maby?

In my basement the laundry / furnace / Water Heater / Storage is in a small section. Over the last month or so I've occasionally noticed that if nobody has been down there and I walk past the furnace / water heater I faintly smell what I believe to be natural gas. Only for an instant. If I sniff around, it's gone.

Tonight I sprayed soapy water on the fittings and see no bubbles other than the suds from the spray and when I questioned what I saw and wiped it clean, I see no bubbles at all with another squirt of water.

Is this worth being concerned about?
Is there a better way for me to detect a leak?

My working theory about why I smell it now is this:
1. We're not running the furnace / AC since the weather has kept the house reasonable.
2. I recently installed a new 'smart' thermostat that lacks the nice circulate function that my previous one did so there's nothing mixing the air.
3. I thought maybe leftover gas from when the water heater burner turns off but that seems a long shot to me.

I'd order a plug in gas detector but those I've seen highly rated on Amazon also have many folks complaining that any hydrocarbon can set them off.

I'm going to e-mail the customer service of my gas company as well to see if they perhaps come out with a 'gas sniffer' as a co-worker called it.

Any thoughts?