Okay, okay, this may not actually be able to kill aliens unless the aliens are very susceptible to anti-bacterial pressurized steam, but this device sure does look like something that would be used to kill an martian or two. This is intended to solely be a pressurized steam cleaner. You fill it up with water, let the heater do its work, point at the grime and shoot the steam. It can be used on anything that gets dirty including car engines. It uses 1200 watts of energy to blast the grime away and with an anti-bacterial cleaning solution the surfaces cleaned will be disinfected as well. This Superheated Anti-Bacterial Steam Cleaner is available for $100.

Superheated Steam Cleaner, via TRFJ