Sensor Nodes (SN) represent a tiny, inexpensive and main constituent part of Wireless Sensor Networks (WSN). As the main source of power supply of SNs is usually battery, which have a strictly limited capacity, the battery life extension is the main driver for energy-efficient WSN design. So, the crucial parameter for energy-efficient applications in WSN is to apply the techniques that greatly reduce energy. There are a large number of already developed techniques that are applied on this field, but the development in this field is still very intense. This paper is a contribution to this field by developing new energy-efficient protocols, much more efficient from the standpoint of energy consumption. These contributions are related primarily to the development of modified Duty Cycle method, RPATS (Reliable Power Aware Time Synchronization Protocol) protocol for time synchronization in sensor nodes, RPLL (Rendezvous Protocol for Long Living) protocol that provides be reliable rendezvous between the sensor nodes, and MART (Multi Address Reliable Transport) transport protocol which allows data to be transferred between sensor nodes in an energy efficient manner.