SSR is used as an electronic switch to control the flow of AC or DC electricity. The solid-state relays are built on opto-coupling technologies since they will provide high resistance and insulation between the input and output circuits. Both of the devices transmit signals while being electrically separated, although there are major variations. 

• The key distinction between optocouplers and solid-state switches is that optocouplers are usually used in low power applications. While solid-state relays are required with even higher power rates up to hundreds of volts or more. 
• Optocouplers typically come as surface mounting devices or leaded semiconductor devices inside limited integrated circuit(IC) packets. In contrast, SSR is found in larger packages and sometimes involving the bolting of a heat-sink.
• In comparison, solid-state relays are also augmented by circuits-often a full circuit block. We can include the LED drive circuit in the optotransmitter, as well as the burst and transient safety circuits in the output. Some solid-state relays have zero-crossing switching for AC signals in AC applications where the output system flips as the AC waveform moves through the zero volt location which also results in the reduction of electromagnetic interference (EMI).