Here are a few alternatives from other fiction:
Halo (Minority Report)
In Minority Report, criminals could be fitted with a small device around the head that numbed the brain, stunning (or at least making compliant) the sentient fitted with the device.
Application of Halo from Minority Report
Explosive Collar (Wedlock)
A collar with a small range receiver and a bit of explosive. Paired to another receiver on a control officer, or another prisoner. When out of range, or on command, the collar will detonate.
Collar exploding from Wedlock
Shock Collar (Thor: Ragnorok)
A similar fitted restraint that can provide shocks ranging from warning to stun to lethal
Shock Collar from Thor: Ragnorok
Quick Freeze (Demolition Man)
Although it seems to have limited or limitless effect in Demolition Man, as required by the scene, the concept is a portable device that flash freezes the prisoner.
Quick Freeze Sphere in Use from Demolition Man
Gravity Guns (Schlock Mercenary)
An extremely-low power gravity gun can be employed as a restraint. Generally controlled by an artificial intelligence, which has sufficient quick thinking to keep the beam tuned as required.
Goober Gun (also from Schlock Mercenary)
A lower tech restraint, firing balls of material that very quickly increase their viscosity from almost nothing (so that it can flow around the target) to very high (keeping the target in place). This viscosity must be layered somehow, allowing a lower viscosity inside so that targets are ripped apart or smothered.
Zero-Point Energy Ray (Incredibles)
A force field that very precisely cancels out velocity and movement.
Zero-point energy ray in use from Incredibles
Alternate Dimension (The New Legends of Monkey, Pokemon, Tron, Superman)
Another option is a portable device that places the suspect/prisoner in a pocket dimension until required for release.
Time Loop (Dr. Strange)
Doctor Strange captures a deity in a small fragment of looped time that would continue looping back on itself until the Doctor negotiated a deal with the timeless deity, after which he released them both.
Frozen Time (Starcraft)
Although later treated as big solid crystals, Protoss prisons were early described as frozen time, given the space and time bending capabilities of that species.
Carbonite (Star Wars)
Not very portable (a facility was required in Empire Strikes Back) and potentially lethal (Darth Vadar asked Boba Fett for assurance that the process wouldn't kill his son in the form of trying it out first on Han Solo), but you could imagine a perfected and miniaturized implementation. The process flash freezes the subject and covers them in a protective coating until intentionally thawed.
Carbonite Freezing, from Star Wars: the Empire Strikes Back
Carbonite Thawing, from Star Wars: Return of the Jedi
In Fringe, one of the government agencies developed and deployed a mist that solidified after a certain number of seconds. It was used to seal dimensional rifts, or imprison monsters.
Amber removed and deployed from Fringe
Neuralizer (Men in Black)
Neuralizers come in many forms and sizes. In addition to temporarily stunning the suspect, it also renders them open to a certain amount of persuasion and provides for a controllable amount of memory erasure.
For completeness. The suspect is wrapped in cloth that eliminates mobility without suffocating the being inside. Optionally can be secured with straps or zippers.