cut a line or release a loaded spring

I want to build a system that will in some way release a loaded spring, that launches some other mechanical parts into motion. However the activation is going to be tricky. Think like a mouse trap. Loading and securing the spring will be by hand, but the release needs to be triggered remotely.

It would be simple enough to have a servo or two crimp down on a line or string, like scissors, but I believe that would require a fair amount of power. This is in a system where size and weight are at an absolute premium. Every inch and gram counts. I was thinking of a hole where a line could pass thru with maybe a pin that punches in to hold it in place until release, but even that I am not quite sure how to approach. Other possibilities might include heating the securement (think low-test fishing line) or otherwise cutting it, but I am not sure how best to proceed.

Thanks for any ideas!

You want to 'pull the pin on the grenade'. use a 5 Volt mini-solenoid driven by a MOSFET, in turn, driven by the arduino pin.

I definitely think the solonoid is the most direct route.

Electrically heating it would be much lighter in terms of hardware, (just a single piece of heater wire as short as possible, and a fet to switch it), but would require being able to put out a pulse of sufficient current to melt the plastic line. Battery state of charge would impact how fast it melted through the plastic line. If you can deal with the power issue, this is probably the way to go. Maybe even dump a cap into it, if your main power source couldn't handle it - of course, then you need a capacitor, which adds weight and space).

It'd take some experimentation to get the parameters of that down, though

By "triggered remotely" could mean a bunch of different things. If pretty much line of sight then R/C would be about the easiest route. There are some pretty small and lightweight receivers out there. Since you are only moving a small distance then even a small servo should be able to handle it by using mechanical leverage. Maybe a little guillotine to cut the line made from an x acto blade.

What is the purpose of the device?

...R

If it's supposed to work like a mouse trap why not just build it like a mouse trap? The catch (the thing you put the bait on) could be actuated by a small electromagnet.