Hardware Monitor – An open letter to the user community

After exactly 14 years, development of Hardware Monitor was discontinued on June 19, 2017.

The product is still in distribution and under full support, but there will be no updates to support new Macintosh systems released in 2017 or later.

This was not an easy decision because Hardware Monitor was a very popular and very successful software product in all the years. We like to share the reasoning behind the decision to discontinue the product with the community of users and loyal customers who loved and supported Hardware Monitor for more than a decade.

Apple has made it very clear that they don't like to tolerate software products such as Hardware Monitor on the long run. They continue to establish technological barriers, both in hardware and in the operating system, to make sensor monitoring in third-party applications as difficult as possible. In addition, the computer architecture for which Hardware Monitor had been originally developed has changed significantly in the last years, so in most environments there is no longer the need to reflect sensor readings to users.


Apple began to add software-accessible sensors to Macintosh computers in August 2002. The technical specifications and known limits for each sensor location have either been published officially, or they could be determined by other means easily. Temperature Monitor, the free variant of Hardware Monitor, was released 10 months later. It become the number one system utility to detect over-temperature situations, a common issue of the PowerPC technology used at that time. Hardware Monitor was published as "pro" version of Temperature Monitor in July 2004. It supported the entire Macintosh product range and could interpret the readings of all built-in sensors with their locations and full specifications. In August 2005, the application Hardware Monitor Remote was added to collect sensor readings for a whole network of local Macintosh systems.

In January 2006, Apple began the switch to Intel processors which since then changed the situation for Hardware Monitor dramatically:

  • Intel processors monitor their own temperature values and use sophisticated technology to control cooling independent of the operating system. In "overtemp" situations, the CPUs will switch to throttling or perform a safe shutdown. System crashes or even hardware defects due to temperature issues could be avoided automatically by the hardware. As of January 2006, Apple started removing all official API (Application Program Interface) that allowed third-party software to access sensors.
  • In April 2008, Apple stopped the publication of  Developer Notes, the official documentation of Macintosh hardware. The technology of Macs basically became a trade secret.
  • For specific Macintosh models released in 2008 and later, the bus hardware is no longer designed to efficiently transport sensor data while a standard operating system is running. Applications that try to access sensor data on such model series can be impacted by a performance penalty.
  • In July, 2010, Apple discontinued the Xserve, the last system which officially supported sensor access via the operating system.
  • In February 2011, the operating system begins to record power and performance warnings for applications that try to collect sensor data on specific Macintosh series.
  • As of June 1, 2012, new applications capable of accessing sensor data must no longer be published through the Mac App Store. The operating system can detect and block Apps that try to override this restriction.
  • In June 2013, Apple replaced Apple Hardware Test by Apple Diagnostics. Technical issues related to sensors are no longer communicated to the user.
  • In the same time frame, Apple stopped documenting detail data of sensors in the Apple Technician Guides, the internal manuals only available to authorized service personnel.
  • In June 2014, applications that try to access the internal core temperature sensors of Intel processors under their own control need special permission from Apple.
  • In July 2016, Apple started to use encryption to protect all remaining diagnostic components that would allow to interpret sensor data.
  • In April 2017, Apple declared to prioritize recycling in closed-loop supply chains over the long-term use of hardware products. As a consequence, sustainability in hardware and software is no longer their goal.

Due to this long list of obstacles continuously established by Apple, it became less and less feasible to continue development of Hardware Monitor, not only under technical, but also under economical, legal, and political aspects. Although we could resolve many of the issues of acquiring sensor readings on new hardware models each year, this wouldn't really make sense if the meaning of these values is so strictly kept under lock and key.