You are using an out of date browser. It may not display this or other websites correctly. You should upgrade or use an alternative browser.
ValveTime.co.uk | Valve News, Forums, Steam
The weapon just before the hovercraft scene looks like a handheld strider gun.
Why? Because when they shot the weapon at the combine that opened the door to the house the combine disappeared like the citizens did when they got shot full strength of the strider's attack. That white outline glow of the body.
That brings up another discussion, what happens to the people that get strider zapped? My first thought was HL2's way of showing teleportation.