We had a mouse in our garage a few weeks ago. I scoured the Internet looking for humane DIY traps. In the end I came up with 3 'designs' which the mouse outsmarted me on every single one.
The first was an empty kitchen tissue roll tube balanced on the edge of a surface with peanut butter on the end stuck out - mouse goes down the roll and tips it up into a waiting tall bucket, mouse eats all the peanut butter, then jumps out of the bucket (not intended).
The second was a 4 pint milk carton with peanut butter in the bottom, rested up against something at an angle with the idea it would be too sloped/slippery to get back out. Peanut butter gone and no mouse.
The last one was the empty 2 litre pop bottle with the top 1/3rd cut off and inverted and stuck in the top of the bottom 2/3. Again, the peanut butter was gone and the mouse somehow got out.
In the end I bought this Rentokil trap from Homebase for about £4.
Used peanut butter again (peanut butter or chocolate spread is recommended - they like 'wet' bait) and within literally 5-10 minutes I'd caught it.
We drove about 5-10 minutes away to a woodland area and released a small but very fat mouse with a penchant for crunchy peanut butter, and it hasn't come back. I read you have to take it a decent way away from your home or else it will return.