The device was round and flat which had incised symbols on its surface. A slight dent at one edge operated a silent mechanism that opened the object like a clam shell. The devise had the appearance of an ornamental mirror, the top half being a polished mirror-like surface and the bottom a pattern of overlapping triangular leaves. The portal was much heavier then it appeared.
This portal was activated when the user concentrated on the mirror surface and imagined a person or place. Once enough focus was made the artifact forced the user into it's surface where it dissolved in front of them as the person was sent spiralling into the vortex. After its use, the device became inert and it was possible to prevent teleportation by covering the mirror based surface.
A study of the incised configurations and the triangles revealing the artifact being of Iconian design, with some similarities with the larger gateways. A computer analysis further determined that the casing of the portal contained a large percentage of neutronium, similar to the gateways themselves. Essentially, it served as a miniature version of the gateway technology capable of transporting individuals many light years away.
In the mirror universe one of the portals was discovered by a Breen, and was subsequently confiscated by the Bajoran Paqu, who in turn gave it to Benjamin Sisko. Sisko gave it to his employer, Kira Nerys, after he accidentally used it and appeared before her. The tested it on one of her slaves who teleported before the Empress of the Romulan Star Empire and was killed swiftly by her Royal Guards. She then made use of it as part of her plans to gain a position of power within the Klingon-Cardassian Alliance. (DS9 novel: Dark Passions)