Advanced technology has been present in the Pathfinder Campaign Setting since the very beginning. The old Pathfinder Chronicles: Gazetteer contains a 1-page entry on Numeria and its crashed spaceship (albeit referred to as a “great metal mountain”). It was inevitable that more detail would be forthcoming. Eventually, Numeria got its own dedicated book, Numeria, Land of Fallen Stars, and an adventure path, Iron Gods, that takes place there and exploits its science fiction aspects.
But adding technology into a fantasy game like Pathfinder takes more than just including some guns and computers in an adventure book. Not only do these things need statistics, but there also need to be consistent rules governing their use. Much like with magic items and spells, players are bound to be interested in having their characters acquire more of such items or even create them themselves. The game needs to have ways to cover such eventualities. Yet a book like Numeria, Land of Fallen Stars simply doesn't have the room to detail these kinds of rules in any extensive manner—not and have any space left over to talk about the setting. The same goes for Adventure Path volumes. Technology needs its own separate book.
That's where the Technology Guide comes in. It provides both rules necessary for integrating technology into a Pathfinder game and a plethora of sample items—big and small, low-powered and high-powered—for villains to use and player characters to acquire. Although the Technology Guide is published as part of the Pathfinder Campaign Setting line of books, this is actually a relatively setting-neutral book. It does focus on fitting its content to the flavour of Numeria and does have occasional references to places in Numeria (and elsewhere on Golarion), but for the most part, the material is generic enough for use in any campaign setting that features technology of any kind. And it's for good reason. As much as I praise world-specific content, there needs to be a baseline for the world-specific to build on. The baseline also allows people to create their own campaign worlds that use technology. It's therefore not surprising that the rules and items from the Technology Guide have been added to the Pathfinder Reference Document, which is usually reserved for material from the setting-neutral hardcover rulebooks.
When adding technology to a fantasy game, one needs to consider carefully its place in the game and the game world. How prominent is it? Is it rare or common? In James Jacobs's introduction to the Technology Guide, he talks about this very thing, and draws comparisons between technology and magic. He rightly points out that magic itself can seem not very magical when it's ubiquitous and so, part of the goal with technology in Pathfinder is that it have a place in Golarion that is similar to the place magic would have in the real world if it existed—one of mysteriousness and awe. In a sense, technology is the “magic” of Golarion. It's a great discussion and, while I know lots of people tend to skip the introductions of books, this one is well worth a read.
The Technology Guide begins with looking at the base rules for handling technology in the game. It looks at the intersection of skills with technology and introduces several new feats. These include four key feats: Craft Cybernetics, Craft Pharmaceutical, Craft Technological Arms and Armour, and Craft Technological Item. These are the technological equivalents of the magic item creation feats. The opening pages of the book also include new spells that interact with technology, several technology-themed archetypes, and a prestige class, the technomancer—a melding of arcane spellcaster with technology. The class is primarily intended for members of the Technic League in Numeria.
The book then gets into the means for creating technological items. The system works in the same manner as magic item creation (although pricing takes into account the fact technological items can be recharged more easily than magic items). Not only does this help simplify the process (by using a system players and GMs are already familiar with) and keep things consistent, it maintains game balance as well. After all, from a strictly mechanical point of view, it doesn't matter whether a character's power comes from magic or technology. The effects are what matter. However, there is one slight difference brought about by necessity. Since technological items are not magical, it wouldn't make sense to include spell prerequisites for their creation, something that is a key balancing point of magic item creation. As a result, technological items require the creator to use specific kinds of laboratories (there are six different kinds altogether). These laboratories also require power, which can be acquired through generators or batteries (both of which are described later in the book).
Of course, in a game that contains both magic and technology, it is inevitable that someone will want to combine them. As such there are rules for this as well. Characters who wish to add magical abilities to existing technological items simply use the standard magic item creation rules. However, it is also possible to create a magic technological item from scratch using a system that combines both processes into one.
The bulk of the book is devoted to the statistics for various technological items. They are divided up into sections of weapons, armour, pharmaceuticals, and technological gear. Within each section, they are listed alphabetically in a manner similar to how other books list and describe magic items, though with a few extra categories. For example, most technological items require power, so each one has a “capacity” statistic indicating the maximum number of charges it can hold at a time.
Since most of the technology in Numeria is actually ancient, with few people understanding how to create new items, the book introduces a special condition for technological items: timeworn. Timeworn items have generally lost the ability to be recharged (meaning when their current charges are used up, they become useless) and often have additional glitches (the inside front cover has charts for determining random glitches). Timeworn items are a good way to maintain the mysteriousness of technology and ensure that it doesn't become too ubiquitous.
The Technology Guide uses a colour-coding system to indicate the relative power of various items. Most items have an illustration and the prominent colour of the illustration indicates the the spell level the item's abilities would be equivalent to if it were a magic item. The colours are based on the seven skymetals, with brown (representing non-skymetal base ores) introduced for 1st-level effects and prismatic (representing all skymetals combined) for 9th-level effects. The system is a nice idea in theory, although in practice, I'm not certain it works all that well (though admittedly, I am not a visual learner, so it may be more successful for people who are). The order of the colours (brown, black, white, grey, green, red, blue, orange, prismatic) is not intuitive and I find it very difficult to remember. As such, if I see a red item, I have to flip back in the book to discover that red represents a 6th-level spell equivalent. Personally, I would much rather there just be a text entry in the item's stat block, saying, “Equivalent Spell Level: 6th”.
There are quite a lot of items in described in the book. There are the staples like various kinds of energy guns, spacesuits, jetpacks, and even a non-copyright-infringing version of a lightsaber, the null blade (which is both technological and magical). Some are simple items like flashlights and fire extinguishers, while others, like the skillslot and skillchip, are more unusual (a skillslot is implanted in a character's brain; then, various skillchips can be inserted, each providing the character with a bonus to a specific skill). Overall, there's enough variety to cover most general needs GMs might have in a campaign. They probably won't cover every possibility, but GMs can easily follow the examples of the ones here to create additional items for their own campaigns.
The final chapter of the book looks at other application of technology—particularly the more powerful ones. It contains an overview of the seven skymetals, as well as rules for radiation and technological traps. There are also rules for artificial intelligences, plus the “aggregate” template, which is for adding an AI to a robot. Finally, there are stats for several technological artifacts. Like magical artifacts, these are examples of the most powerful items and cannot be easily created like other items. Unlike magical artifacts, however, technological ones can be destroyed like any other items and may even be quite fragile.
Overall, the Technology Guide provides gamemasters with the information and items they need to add technology into their fantasy games. It's not particularly exciting or innovative, but that's not really its point. Instead, it forms the necessary baseline for other books to build upon, much like the Core Rulebook provides the baseline rules for the entire game. If you want technology in your games, it's a book you really can't do without.