BACnet reliability, event state and device status

Updated 7 November 2026

Short answer

Reliability says why a value may be wrong; Event_State says whether an object is in alarm; System_Status says what the device itself is doing. All are numbers on the wire. Examples: 0 = no-fault-detected, 1 = no-sensor, 2 = over-range.

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Reliability (25)

Number	Reliability	Notes
0	no-fault-detected	The value can be trusted.
1	no-sensor	No sensor is connected.
2	over-range	The input reads above its range (often an open or failed sensor).
3	under-range	The input reads below its range (often a shorted or failed sensor).
4	open-loop	Open circuit on the input or output.
5	shorted-loop	Short circuit on the input or output.
6	no-output
7	unreliable-other	The device knows the value is wrong but gives no specific reason.
8	process-error
9	multi-state-fault
10	configuration-error
12	communication-failure	The device lost contact with whatever supplies the value (a sub-network, wireless sensor or gateway).
13	member-fault
14	monitored-object-fault
15	tripped
16	lamp-failure
17	activation-failure
18	renew-dhcp-failure
19	renew-fd-registration-failure
20	restart-auto-negotiation-failure
21	restart-failure
22	proprietary-command-failure
23	faults-listed
24	referenced-object-fault
25	multi-state-out-of-range

Event state (6)

Number	Event state	Notes
0	normal
1	fault
2	offnormal
3	high-limit
4	low-limit
5	life-safety-alarm

Event type (21)

Number	Event type	Notes
0	change-of-bitstring
1	change-of-state
2	change-of-value
3	command-failure
4	floating-limit
5	out-of-range
6	complex-event-type
8	change-of-life-safety
9	extended
10	buffer-ready
11	unsigned-range
13	access-event
14	double-out-of-range
15	signed-out-of-range
16	unsigned-out-of-range
17	change-of-characterstring
18	change-of-status-flags
19	change-of-reliability
20	none
21	change-of-discrete-value
22	change-of-timer

Device status (System_Status) (6)

Number	Status	Notes
0	operational
1	operational-read-only
2	download-required
3	download-in-progress
4	non-operational
5	backup-in-progress

Values come from the open-source bacnet-stack 1.6.1 (bacenum.h), which follows ANSI/ASHRAE Standard 135, and were cross-checked one by one against two other independent BACnet stacks (bacpypes and @bacnet-js/client). Entries marked (newer) are in bacnet-stack only, because the other two stacks predate them. Numbers 0-255 (and the higher ASHRAE ranges) are standard; vendors may use proprietary numbers above them.

More BACnet reference

Easy BACnet reads these values straight off the device from an Android phone and shows them as words, not numbers.