Intermittent supervisory trouble, a corroded 20-year-old conduit run, and a $10,000 trenching estimate — resolved for under $2,000 with wireless supervisory monitoring.
A client called us in after their fire alarm panel started throwing a supervisory trouble condition and beeping, on and off, with no obvious pattern — except one: it was consistent during and after rain. On investigation, the source was a Post Indicator Valve (PIV) roughly 100 feet from the main building, monitored through underground conduit.
Our conclusion: water had penetrated the underground conduit over time and was causing intermittent shorts in the supervisory circuit conductors — a common failure mode once older conduit runs lose their seal.
The building was at least 20 years old, and once water gets into an aging underground conduit run, it doesn't just short the cable — it also tends to swell, corrode, and jam the conduit itself. We attempted to pull new cable through the existing run and confirmed what we suspected: it was seized solid. Trying to force it risked collapsing or further damaging the conduit.
Given the cost gap, the client chose the wireless route — saving more than 80% versus trenching, without compromising code compliance or reliability.
The SignaLink Bridge is a fully supervised, UL 864 10th Edition and ULC S527 listed wireless system built specifically for monitoring dry-contact fire protection devices — tamper switches, flow switches, and valve supervisory switches like the one on this PIV. It's CSFM-listed for use in California. A wireless transmitter pairs to the device being monitored; a wireless receiver at the fire alarm panel reports the switch's state as a standard supervised dry-contact input, compatible with any existing fire alarm control panel.
It communicates on the 2.4 GHz band with a clear-line-of-sight range of roughly 800 feet — more than enough for a PIV 100 feet from the building — and is housed in a NEMA 4 (IP66) weather-resistant enclosure rated for outdoor use. Each transmitter runs on a pair of AA lithium batteries, which the system's setup tool can check remotely without opening the enclosure.
Trenching is a one-time capital cost with no ongoing maintenance. The wireless system costs far less upfront but runs on batteries, so we've laid out both the initial cost and an estimated 5-year total, including periodic battery swaps, for a fair comparison.
Maintenance figures are estimates for planning purposes — actual battery life depends on transmission frequency and site conditions, and we check battery health at every inspection visit. Even at the high end of estimated battery maintenance, the wireless approach still costs roughly 80% less over five years than trenching.
This job is also a good example of why AllTime Systems never runs standard FPLR fire alarm cable underground — even inside Schedule 40 or 80 conduit. Conduit is not a guarantee against water intrusion over the life of a building; joints settle, seals degrade, and ground water finds its way in eventually, exactly like it did here. When we run cable underground, we use cable rated for direct burial, engineered to handle prolonged wet contact, not just cable that happens to be inside a pipe.
A smaller detail worth knowing if you're planning similar work: fully buried horizontal conduit runs are typically fine in Schedule 40, since the surrounding earth protects the pipe. But wherever conduit stubs up above grade — say, through a landscaped area where a mower or line trimmer could strike it — code calls for the heavier-wall Schedule 80 at that exposed transition. It's a small spec detail, but it's exactly the kind of thing that prevents the next avoidable service call.