So any creature with a power point reserve or other brown unicorns can hear it? How do we want to specify psionic creatures since we usually stick psionics in a sidebar?
Should we include creature with Psi-Like Abilities (since not all have power point reserves) and non-psionic telepathic abilities such as a
read thoughts or
telepathic bond spell or SLA?
How should we write this up, perhaps something like:
Psychic Warning Fence (Psi): A male brown unicorn can create an invisible barrier of mental energies around an area up to
X in size. Psychic creatures that cross this barrier receives a telepathic warning that it is entering the a brown unicorn's territory, other brown unicorns receive the additional information of the stallion's name. The Psychic warning fence warns any creatures with a psi-like ability, psionic characters with a power point reserve, and non-psionic characters with the telepathic abilities (such as the ability to cast
read thoughts or
telepathic bond as a spell or spell-like ability). The telepathic ability need not be active, the intruder need merely have the potential to use telepathy, so a wizard who's prepared
read thoughts but has not cast it would receive a warning. The psychic warning fence lasts for a duration of
Y hours, and can be dispelled as if it were a psi-like ability with a manifestation level of
Z.
...or we could just drop it, since it's a colourful background-ability without that much utility.