The Irish Penal Chaplet was developed during the Penal Era in Ireland, which dates from about 1540-1731. At that time, the Church of England required a uniformity of religious practice resulting in the persecution of many Irish Catholics. Evidence of this era can still be found today in the form of monastery and church ruins scattered throughout Ireland.
Consequently, the possession of a rosary became a sign of rebellion, even punishable by death. The Irish Penal Chaplet consists of 10 beads (a decade) plus one additional bead strung on a cord with a ring at one end. The ring could easily be attached to the finger and hidden in the hand and/or up a sleeve, allowing one to pray the rosary without being detected.
Bottom photo link: http://www.etsy.com/listing/60124044/handmade-irish-penal-era-rosary