€312,000.00
HM12 The Guardian is the first Horological Machine conceived entirely by Maximilian Büsser and Maximilian Maertens, and the first major HM without Eric Giroud on exterior design. The brief was almost childlike — what if a robot head were a watch — and Maertens spent four years turning it into a Grade 5 titanium case whose six synchronized shields physically open and close across the face. Inside sits an in-house automatic with a double winding rotor and a flying tourbillon beneath a sapphire aperture at twelve; quick-release lugs even let the watch detach and mount onto a companion robot built by L'Epée 1839. It reads less like a wristwatch than a small mechanical character.
HM12, subtitled The Guardian, is the first Horological Machine developed entirely by Maximilian Büsser and Maximilian Maertens — and the first major HM without Eric Giroud shaping the exterior. It arrived in 2025 as three limited runs of twelve in green, blue and purple: 36 watches in all.
The case is a robot head in Grade 5 titanium. Six synchronized shields open and close across the face as a complication you can watch happen, and the whole object is engineered so the watch can detach from its strap and clip onto a companion robot built by L'Epée 1839 — one system, two mechanical beings.
Under the shields runs an in-house automatic of 646 components and 86 jewels, with a double winding rotor and a flying tourbillon visible through a sapphire aperture at twelve. It also shows instantaneous jumping hours and trailing minutes; the drama is engineered, not decorative.
Movement timing was recorded on our bench before this watch was offered — the figures are below. A full condition report for this specific example, covering case, dial and service history, is available on request.
Before it left our bench, this movement was put on a timing machine and read in six positions. Here is how it performed.
| Rate | Beat error | Amplitude | |
|---|---|---|---|
| Averageacross six positions | +1 s/day | 0.2 ms | 285° |
| Deviationsteadiest to least steady | 7 s/day | 0.4 ms | 32° |
Average is the mean across dial up, dial down and the crown at up, down, left and right. Deviation is the spread between its steadiest and least steady position — a read on how consistently it keeps time, not just how fast it runs.
