Sacramentals are sacred signs instituted by the Church. They prepare men to receive the fruit of the sacraments and sanctify different circumstances of life. Catechism #1677.

What do they do?
1.Deliver and protect our person and goods from the harmful influences of Satan. Christ gave His Church the power to expel evil spirits. "He gave the power to heal sickness and to cast out devils." (Mk. 3:15). The Church has always made use of this power and hence the means she employs for the casting out of evil spirits, are the sacramentals, such as the invocation of the Holy Name of Jesus, the Sign of the Cross, Holy Water, and in some cases, exorcism, They also protect from diabolical attacks-hence, the Church blesses newly built houses, stables, barns, ships, cars, and other things so that the devil may be kept away from these places and not exercise an injurious effect upon them. Therefore, as well as blessing ourselves with Holy Water and the Sign of the Cross, we should have our houses, cars and other things blessed with the Sacramentals, showing that they are dedicated to God.

2. Avert from evils due to natural causes-they are remedies against all sicknesses, weaknesses and frailties of the body, and are sure to effect relief if this is beneficial for the soul. Sometimes a sickness may be there for God's will for us: "Why do you seek aid from physicians when you are sick, and not from Christ, as if He were not also the physician of your body?" (St Ephrem).

Sacramentals are remedies against epidemics, storms, etc., but only on the condition that the aversion of any evil brings no injury to our salvation. Eg. St. Benedict blessed a chalice of poisoned wine with the Sign of the Cross, and it fell to pieces.