If you are looking for totally free sound effects, you may be in the right place. If you are looking for free sound effects of explosions, laser weapons, and alarms you have definitely come to the right place!
My library of sound effects currently contains 96 free effects (25 alarm effects, 35 explosions, and 36 laser effects.) You can preview and download all the effects as WAV files (16bit 44.1KHz Stereo), Vorbis OGG files (encoded at the bitrates 128kbps and 64kbps), and MP3 files (encoded at VBR 190kbps.)
To make browsing easier you can click on this link to browse the sound effect library with only the free ones visible =)