Alarm spell description mentions "Tiny" as a minimum size threshold:

an alarm alerts you whenever a Tiny or larger creature touches or enters the warded area

It says "a Tiny or larger creature", not just "a creature". I assume, that means there are creatures beyond size categories, like flies or mosquitoes, which are too small to be taken in consideration in this case (and other cases, including combat, space control, etc.). What maximum size do they have?

Related question: How tiny is a Tiny spider?


3 Answers 3


There is no listed category smaller than Tiny.

Most likely the spell is worded this way so that the Alarm doesn't go off when you are approached by creatures that aren't really "creatures" in the D&D sense; insects and such.

The maximum size of these seems up to the DM, given that they likely don't have any stats at all.

(You'd be hard pressed to find any area with no creatures at all in it. And if you found one, you probably wouldn't want to sleep there...)

  • 2
    \$\begingroup\$ You basically rephrase the Q. I know that Tiny is the smallest category. My assumption was there are smaller creatures exist (insects and such). The Q was about their maximum size limit. \$\endgroup\$
    – enkryptor
    Sep 25, 2017 at 13:27
  • 4
    \$\begingroup\$ My answer to that is "up to the DM", given that they have no stats. \$\endgroup\$
    – Erik
    Sep 25, 2017 at 13:30
  • 1
    \$\begingroup\$ When you say 'so that the Alarm doesn't go off' you make it sound like ants don't trigger 5e's Alarm, when they, in fact, do (as your answer otherwise makes clear). \$\endgroup\$ Sep 27, 2017 at 5:22
  • 3
    \$\begingroup\$ @thedarkwanderer I would say that a creature with no stats is not "Tiny or larger", so they don't trigger the alarm. \$\endgroup\$
    – Erik
    Sep 27, 2017 at 5:30
  • \$\begingroup\$ I am going to offer an opinion, that you may or may not wish to fold into your answer, that the reason for the Tiny threshold is the anti munchkin effect: someone trying to find a loophole for wild shape or shape change or polymorph so that they can bypass an Alarm spell due to a rule exploit ... the devs know what munchkins are. \$\endgroup\$ Oct 5, 2017 at 4:03

Tiny is the smallest creature size

Your question states an assumption within it that may not be correct:

I assume, that means there are creatures beyond size categories

However, there is no reason to make that assumption. The published material by WoTC lists all of the current creatures with stat blocks. If there are no stat blocks of creatures of different sizes, then the assumption is that is the complete list.

The table in the MM (page 6) lists creature sizes and space control. Tiny is the smallest and Gargantuan is the biggest. Those are the only available sizes for DMs and Players to use without making home variants.

The text language of "Tiny or Larger" doesn't make the assumption that there is a smaller size. It simply states that ANY creature will trigger it. Yes, it might be have been simpler to say it that way, but I am not a WoTC editor :)

Space Control vs Physical Size

Also, the size categories are about space control and not purely physical size. Your creatures may be of varying actual dimensions, but the size table is for space control. But given the limitations of the table, even if you're working with a Scorpion (which is pretty darn small), it falls under the Tiny category and gets triggered by Alarm.

There isn't a differentiation in the Monster Manual, DMG, or PHB about category size (space control) and actual size of creature. Those are blended under Category Size. Whether or not the intent is that there is an 'insignificant' creature if it is smaller is not known, and can't be made officially. The intent is more likely that any relevant creature is at smallest Tiny. That also generally holds up against the list of creatures in the Monster Manual and PHB.

Singular insects (other than scorpions), aren't listed, so the concern of a single insect getting through an alarm isn't one. Especially since that insect is Tiny. You can't polymorph into a different insect type or do anything with one in a way that would allow you to use it to bypass Alarm.

DM Decisions

The DM, as always, can create new creature sizes and stat blocks to accommodate for anything they'd like to add or change at their table. However, as you've raised with Alarm, doing so may introduce unforeseen effects that aren't planned for by WoTC but should be considered when implementing homebrew.

Alarm currently works to stop all creatures from entering that meet it's condition. If you create a new creature that breaks Alarm by either always setting it off or allowing it to bypass it, then that particular Homebrew needs to either be accepted or you have to adjust the stat block or the spell to accommodate for it. But the RAW here is dependent on published stat blocks and creatures.

  • 1
    \$\begingroup\$ "Tiny" is the smallest creature size category indeed, but is it the smallest creature size? I guess RAI "a Tiny or larger creature" restriction means that trivial flies or mosquitoes can't trigger the alarm. \$\endgroup\$
    – enkryptor
    Sep 25, 2017 at 13:25
  • \$\begingroup\$ @enkryptor Added some additional points to answer that. \$\endgroup\$
    – NotArch
    Sep 25, 2017 at 13:31
  • \$\begingroup\$ "You can't polymorph into an insect" - hence the question.. I've edited the Q a bit to be more clear \$\endgroup\$
    – enkryptor
    Sep 25, 2017 at 14:21
  • \$\begingroup\$ @enkryptor saw the edit and adjusted accordingly. Ultimately, it comes down to we have take what's given to us. WoTC doesn't give stat blocks for creatures of anything beyond Tiny, and only lists Tiny as the smallest size. There's your published RAW limitation. \$\endgroup\$
    – NotArch
    Sep 25, 2017 at 14:24
  • \$\begingroup\$ So, do you mean there are no insects in any DnD setting because MM doesn't mention them? Or do you mean there might be insects, but MM isn't "all encompassing" and doesn't describe them just because they are not significant? If the latter, then these insects are "creatures beyond size categories". \$\endgroup\$
    – enkryptor
    Sep 25, 2017 at 14:32

While the question is tagged as dnd-5e, since there is no RAW 5e answer published yet, I will suggest a solution to guide DMs who happen to come by this question.

A 5e-compatible answer is present in the earlier editions, for example the 3.5e. If you compare the SRDs for 3.5 and 5th editions, you will see that the creature sizes are defined exactly the same way for the categories that are present in 5e. For example, consider size category Huge. According to 3.5e SRD, the space it occupies is 15ft. 1 Likewise Huge creatures occupy 15ft by 15ft according to the 5e SRD (page 254 on SRD 5.1 pdf) 2.

It appears like the 5e designers decided to simplify the game by getting rid of size categories smaller than Tiny and larger than Gargantuan. It is possible that the wording in the Alarm spell was forgotten to be updated, as the 3.5e SRD also has the exact phrase 3: "each time a creature of Tiny or larger size".

So if you like, you can use the size categories in 3.5e to guide your alarm spell and rule that creatures shorter than approx. 1 ft and/or lighter than 1 lb might not trigger the Alarm.

This interpretation is also roughly consistent with the version of the spell as it existed in even earlier editions (AD&D 2e PHB pg 131, AD&D 1e Unearthed Arcana pg 51), which explicitly states: "any creature larger than a normal rat - anything larger than about one-half cubic foot in volume or more than about three pounds in weight" would trigger the spell.


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