This paper presents the evaluation on energy consumption of power saving mechanisms in recent IEEE 802.15.4 Low-Rate Wireless Personal Area Network (LR-WPAN) systems. The LR-WPAN applications share a common system requirement of high energy efficiency through power saving mechanisms to prolong battery lifespan. First, the recent IEEE 802.15.4 standard amendments including, but not limited to IEEE 802.15.4/4e/4f/4g/4j/4k/4m and their targeted applications are listed and discussed. Then, the applications are categorized based on different energy consumption models which are interconnected with the radio operations of the proposed power saving mechanisms. Next, addressing pervasive demands and respective energy consumption models in multiple application scenarios, three power saving mechanisms for LR-WPAN are proposed and evaluated taking into consideration realistic parameters. As a result, it is found that the power saving mechanisms are capable of supporting battery lifespan up to typically 3 years. Out of the three proposed mechanisms, two are found to be more suitable for deployment of symmetrical energy consumption model where all devices share similar burden of radio operations, while one is found to be otherwise, optimized for asymmetrical energy consumption model where some devices have larger burden as compared to others.