Monitoring
A server room needs alarms on its UPS and batteries, temperature at the rack inlets, humidity, water leaks and door access, with smoke detection beyond the building's own system where the risk justifies it. Each sensor goes where the threat starts, and each alarm needs a threshold and a person to receive it.
The UPS and battery alarms, because they decide whether the room survives a utility failure. A UPS reports its own power quality, load and battery health, and Vertiv states that approximately 37 percent of all UPS system failures are battery related. After the power path, the threats Schneider Electric lists for the room itself are excessive server intake temperatures, water leaks, and unauthorised or careless access. Built-in alarms already cover the UPS, the cooling units and the code-required fire system; the rest of the room is usually unwatched unless sensors are added.
Those UPS alarms are only useful when they reach someone. The remote UPS monitoring page covers alarm routing and response; this page covers the sensors around it.
At the front of each rack, where the equipment draws its air, at the top, middle and bottom. That is Schneider Electric's basic placement in White Paper 102, which points to the ASHRAE guidelines for it. Room-level readings near a cooling unit say little about the server at the top of a rack at the end of a row, which is often the warmest inlet in the room.
ASHRAE's recommended inlet range is 18 to 27 °C for all four of its air-cooled equipment classes; its allowable range for class A1 is 15 to 32 °C. Schneider Electric suggests starting alarm thresholds of 20 °C low and 25 °C high, then adjusting each sensor to the equipment it watches and to its mounting position.
Because a fast rise announces a cooling failure before any fixed threshold is crossed. Schneider Electric's paper states that alerting on the rate of change gives a quicker indication of failure than a snapshot value, and that a change of 5.6 °C in a 5-minute period is a likely sign of a failed cooling unit. ASHRAE limits the change itself for most IT equipment: no more than 20 °C in an hour and no more than 5 °C in any 15-minute period. A rate-of-change alarm turns a slow drift and a sudden failure into two different messages.
With one sensor per cold aisle, at the front of a rack in the middle of the row, away from the direct outlet of a cooling unit. Low humidity raises the risk of static discharge; high humidity brings condensation. ASHRAE's recommended envelope runs from a dew point of -9 °C to a dew point of 15 °C and 60% relative humidity, and Schneider Electric suggests starting thresholds of 40% and 55% relative humidity. Cooling units report humidity too, but at their own return or supply, not where the servers breathe.
Around every source of water and at every low point. Schneider Electric's placement: leak rope around each cooling unit and cooling distribution unit, under raised floors, and along any other leak source such as pipes; spot sensors in drip pans, in small rooms and closets, and at low spots. A leak under a raised floor can travel a long way before anyone sees it, and the UPS, its batteries and the power cabling are often on that floor.
For a room whose UPS batteries share the space with the servers, battery temperature matters as much as inlet temperature. ASHRAE gives 25 °C as the ideal for lead-acid batteries and, as a rule of thumb, halves their life for every 8 to 10 °C above it; the UPS battery life guide covers the effect in detail.
Through aggregators, thresholds and an escalation list. Schneider Electric recommends aggregation points spread through the room, each with its own alert and notification capability, rather than every sensor reporting to one central box. Each sensor should allow several thresholds, for informational, warning, critical and failure levels, and each level its own recipients: a humidity event might send an email to the IT administrator, while a smoke sensor triggers a call to the fire department.
Alerts travel by email, SMS text, SNMP traps or posts to HTTP servers, and each should name the sensor, its location and the time. A system that escalates an alarm to a higher level when nobody resolves it within a set time is worth more than one with more sensors. The room's UPS itself is covered in the server room UPS guide; replacement batteries for the UPS in a server room are on the data centre UPS battery page.
ASHRAE recommends 18 to 27 °C at the IT equipment air inlet. Schneider Electric suggests starting alarm thresholds of 20 °C and 25 °C, adjusted per sensor.
At the front of each rack, where the equipment draws air: top, middle and bottom. A single wall sensor misses the warmest inlets.
ASHRAE's recommended envelope runs from a -9 °C dew point to a 15 °C dew point and 60% relative humidity. Schneider Electric suggests alarms at 40% and 55% relative humidity to start.
Not in normal operation, according to Schneider Electric, because VRLA batteries do not release hydrogen in normal use. Wet-cell battery rooms have their own code requirements.
By more than one route, such as email, SMS and SNMP traps, with the sensor name, location and time in each message, and escalation when an alarm is not resolved.
Sources, checked 2026-10-04:
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