[RPG] Can an Unseen Servant trigger an Alarm spell, and can said Alarm be customized

Technically, yes.

There is a speed figure for an Unseen Servant, along with a list of available actions (emphasis mine).

It can run and fetch things, open unstuck doors, and hold chairs, as well as clean and mend. The servant can perform only one activity at a time, but it repeats the same activity over and over again if told to do so as long as you remain within range. It can open only normal doors, drawers, lids, and the like. It has an effective Strength score of 2 (so it can lift 20 pounds or drag 100 pounds). It can trigger traps and such, but it can exert only 20 pounds of force, which is not enough to activate certain pressure plates and other devices. It can’t perform any task that requires a skill check with a DC higher than 10 or that requires a check using a skill that can’t be used untrained. Its speed is 15 feet.

There is nothing that prohibits double move for an Unseen Servant. One can even argue that it can literally run, but even double move equals 30 feet per round and is sufficient to catch up.

As a side note, while the speed is not listed as fly speed, certain low-priority sources (Sage) speculate that Unseen Servant can be directed anywhere within spell range, provided there is a line of effect to the target location.

Let's dive into this spell a bit.

Unseen Servant

"....creates an invisible, mindless, shapeless force that performs simple tasks at your command... The servant springs into existence...on the ground within range. ...you can mentally command the servant to move... and interact with an object. ...can perform simple tasks that a human servant could do to the best of it's ability..."

Now that I've enforced the relevant sections of the text; we can start to answer your questions.

1. Can an Unseen Servant be interacted with?

   • Since the Unseen Servant is not only mindless; possessing no intelligence of it's own and unable to act of its own will; it simply follows the most basic of commands, aided in it's endeavors by the same magic that binds it to you; but is also invisible, as well as shapeless, you would have to have a way of divining the servants location or seeing invisible creatures before you can even attempt to ponder interacting with it. Since it DOES occupy a space, however, this leads me to believe that force applied upon it CAN effect it. It can be pushed out of the way and such.

2. Can it be commanded to 'hang on' or otherwise interact with another creature?

   • It's strength score is 2, that's a -4 . Looking at the relevant entry (do not currently have access to it) we find that a -4 is extensively lower than the average human being. This creature can do simple tasks to the best of it's ability , and it's -4 strength ability probably does not allow for what you are asking.

3. Can Unseen Servant displace substances?

   • Considering that the Unseen Servant is shapeless, as made clear in the first line of text, generally we would have to rule that there is no shape it possesses in which it WOULD displace any kind of matter, liquid or otherwise. Since the spell does not explain HOW this mindless, shapeless magical servant affects the items it does interact with; such as cleaning and folding clothes, we must assume it does so through magical means, NOT with any sort of invisible appendages or form that it possesses.

In closing; this is one of the very few spells that leaves me with holes in it's logic. It is invisible. This one is easy enough. If it DOES possess some sort of form, then you can not see it by mundane means. It is mindless. Possessing of no intelligence or mental acuity, and so it can only follow commands to the best of its abilities, which are very poor and extremely under your average human beings range of capabilities. It is shapeless. This is where the most confusion appears. Possessing of no shape, no substance that comprises it's physical being; whether invisible or not. If it has no shape, yet occupies a space on the ground, how does it interact with the items it must interact with in order to do it's job as per the spell permits? I can't logic this one away. 'Magic' seems to be the only thing holding this together.