The spell clock is a fusion of clockwork and magic that works as a timer for stored, long-duration spells on a particular place or creature every hour. A cheaper version of the spell clock is a single-use item that serves as a fuse for a dangerous spell to create havoc with a slight delay.
A spell clock doesn't look like much; it is usually a square box with a face of enameled pewter or brass covering a simple spring-driven mechanism, with a set of a dozen gears. Its face has either two or three gold or black hands that show the time remaining until the next spell it contains is released. The enamel protects the clock face from moisture, and the exterior casing is made either of rot-resistant tropical hardwoods from Xen'drik, of sturdy brass, or sometimes of corrosion-resistant-but-ugly grayish nickel.
When operating, a spell clock always produces a loud ticking noise. It can be heard in the same room without requiring a Listen check, with DC 5 Listen check through a door, and with DC 15 Listen check in neighboring rooms. Some claim to hear the sound of a spell clock's ticking even when it is muffled and hidden. This is its one weakness when used as a timer for offensive spells, as even when kept in a soundproofed trunk full of wool or blankets, it can be heard with a DC 20 Listen check.
Use and Powers
Most spell clocks are steady, repeating devices that cast relatively non-violent spells. A few are disposable.
A steady spell clock can be used as a simple trap, by casting (for example) a wall of stone at a certain time after it is set ticking, thus possibly trapping creatures in a passageway beyond the spell clock. It can be used to buff creatures who know (or are commanded) to visit it on a regular schedule. It is as flexible and powerful as the long-duration spells it casts.
Typical spells used in spell clocks include: antimagic field, antiplant shell, antilife shell, daylight, dispel magic, energy conversion, elemental swarm, flame arrow, fog cloud, foresight, heroism, glibness, invisibility, invisibility purge, keen edge, magic circle against evil, protection from spells, repel vermin, resist energy, spider climb, stoneskin, telepathic bond, teleportation circle, tongues, web, and the various wall spells.
Disposable spell clocks typically cast evocations such as fireball or burning hands within a set period of time after a trigger (typically, a door opening or a noise within 5 ft.) sets them off. These are just proximity or time triggers on standard traps and require little more elaboration here. A few cast summoning spells once set in motion; the summoned creatures attack the people nearby.
Stopping a spell clock requires the use of a command word or a successful Use Magic Device check (DC 20 + creator's spellcasting level).
The material components for spells stored within a spell clock are usually included in the construction. The clock cannot contain spells that require the material components to be somewhere besides the caster's hands (for example, animate dead or mark of justice).