From BiblePortal Wikipedia

Charles Buck Theological Dictionary [1]

Or ACOMETI, an order of monks at Constantinople in the fifth century, whom the writers of that and the following ages called Watchers, because they performed divine service day and night without intermission. They divided themselves into three classes, who alternately succeeded one another, so that they kept up a perpetual course of worship. This practice the founded upon that passage, "pray without ceasing, "  1 Thessalonians 5:17 .

Cyclopedia of Biblical, Theological and Ecclesiastical Literature [2]

( Ἀκοιμηταί , Watchers ) , an order of monks instituted at the beginning of the fifth century by Alexander, a Syrian monk (Burger, De Acoemetis, Schneeberg, 1686). They were divided into three classes, who performed divine service in rotation, and so continued, night and day, without intermission. They were condemned by a synod held at Rome in 534 for maintaining that Mary was not the mother of God. Helyot, Ordres Relig. 1, 4 sq.

( Ἀκοιμήται , Sleepless), a name given to certain monks who, divided into three classes, sang the Holy Office in turns, so that it continued day and night without intermission. The order was probably founded by an officer of the imperial household at Constantinople, named Alexander (q.v.) about the middle of the 15th century. The first monastery which he established was on the borders of the Eupthrates, after which he returned to Constantinople, and founded one on the Dardenelles, where he died, about A.D. 430 (or 450). After his departure from the monastery on the Euphrates, the Acoemetae had for their abbot John, who was succeeded by Marcellus. Among the distinguished persons who supported the order was Studius (q.v.), a Roman nobleman, who built a monastery for their use at Constantinople. This was called, after him, Studium, and the monks of it Studitce. There was another monastery, founded by St. Dius, which also became theirs.

Their "hegumei" (or president), Cyril, made complaints at Rome against Acacius (q.v.) which resulted in his excommunication. Meanwhile Peter the Fuller, who had been expelled from their order, had become schismatic patriarch of Antioch, and made common cause with their opponents. In the following century they became entangled in the Nestorian heresy, and the emperor Justinian caused them to be condemned at Constantinople. In 534, in a synod held in Rome, pope John II excommunicated them for denying the proposition Unus e Trinitate passus est carne, and maintaining that the Virgin was not the Mother of God. This monastic institution soon passed into the West, was established in the Abbey of St. Maurice of Agasine, in Valais, by Sigismund of Burgundy, and was confirmed by a council, A.D. 523. It was also established in the monasteries of St. Martin at Tours, Luxeuil, St. Riguier, and others. The perpetual service of the Accemetam was called by the Latins Laus perennis. See Evagrius, 3, 18, 21; Moreri, Hist. des Odres Monast. (preface, p. 238); Bingham, Christ. Anti. bk. 7 ch. 2, § 10.

The Nuttall Encyclopedia [3]

An order of monks in the 5th century who by turns kept up a divine service day and night.