I am working on a project that involves a GSR sensor. Using Arduino, I created the GSR sensor so the finger would be placed on a copper coin which is attached to the end of the wire. Is it 100% safe to get data of skin conductivity when the finger is essentially touching the electrically active wire? If not, is there an alternative to make it safe?
Generally it is safe to touch conductors in low voltage powered circuits if they are battery powered or electrically isolated from household AC. Modern computer power supplies are usually so isolated, but a laptop disconnected from the AC line is always safe.
You need two connections to measure skin conductivity.
Most regulations consider anything less than 48V to be safe, and anything greater than 48V has to be insulated & isolated from human touch.
...One thing that can be tricky is inductors (including motors) because even with a small battery you can generate enough voltage to get a shock. That's how those prank/shock gadgets work. It's also how a 12V battery generates enough voltage for a spark plug in a car, and that IS dangerous!
Actually as someone who has worked on cars for a few decades, While a automotive ignition lead to the spark plug will shock the crap out of you, it typically won't drop you to the ground. Typical stock applications range anywhere from 18k-40k volts, but keep in mind there is zero amperage behind it.
A common old skool prank was to take a ignition condenser, stick the lead into a spark plug wire and crank the engine over thus charging the condenser. Then as you walk through the shop you toss it to you buddy and say catch...Inevitably when they catch it the lead will touch the casing and short out and shock the ship out of your buddy. All in good fun
So to answer the original question, no there is no danger in touching your very low voltage coin sensor.