Garden hedges, which used to be cut with a knife or with pruning shears, can now be cut with a powered hedge trimmer. The power source can be gasoline or electricity. The former tend to be more powerful but can be heavier and more difficult to start. The latter tend to be lighter and less powerful, but also less polluting. Powered hedge trimmers are generally designed with safety devices such that they only work when both of the operator's hands are on the handles.