You have to use the contingency option, which isn't detailed in the limited teaser. It allows the activation of a spell up to one week (at least the last version I saw). Furthermore you have to look for the required spell effects in the spell lists.
Alarm: Illusion Sound/Illusion Air
Fire Trap: Evoke Fire
Magic Mouth: see Alarm
Symbol: Depends on the effect
Symbol of Death: Evoke Death
Symbol of Sleep: Charm [Creature]
For more persistent spells you have to use Permanent Spell or another Item Creation feat.
Oh. Elements of Magic is being revised. In the original version, the spells you mentioned aren't that easy to do. In the revised edition, they will be. The revised edition isn't out yet, but you can download a teaser on the EN Publishing site.