The lead roof has an alarm system because lead is stolen: sensors on the sheets that feel a footstep and log where, and a camera on the tower looking down the length of the roof. Every night at about one the sensors log a walk from the east end to the tower, steady, at a person's pace, and the camera shows moonlight on empty lead.
I am the churchwarden who deals with the insurers, which is how the roof alarm became mine.
How the system works.
The sensors are on the lead sheets along the nave roof, and they register vibration and log which sheet and when. A footstep on the roof is a sequence of sheets in order, and the system alarms on that pattern, because a sequence is a person and a single hit is a crow.
The camera on the tower is infrared at night and covers the whole nave roof from the east gable to the tower foot.
At about one every night the sensors log a sequence. East end to the tower foot, sheet by sheet, at the pace of a person walking, about forty seconds for the length of the roof.
The alarm goes to the monitoring company, and for the first year they called me, and I went out with a torch, and there was nobody on the roof.
The camera shows nobody on the roof. Moonlight or rain or dark on the lead, and the sheets logging a footstep in order underneath it.
What has been checked.
The sensors. Recalibrated, then replaced, and the company's engineer set them so that a cat would not trip them and a person would, and tested that himself on the roof, and the log recorded his walk exactly as it records the night walk.
The camera. Cleaned, then replaced with a better one. The better one shows a better picture of an empty roof.
The lead. It has been walked by the architect, and there is nothing on it: no loose sheet, no animal run, no branch. The yew was cut back in 2020 for exactly this reason and the walk carried on.
Wind, thermal movement of the lead, rain. Lead does move and the sensors know the difference, and the walk is on still nights and wet nights alike, at the same pace, in the same direction, always towards the tower.
The pace.
I have timed it from the log on thirty nights. Forty to forty three seconds for the roof, which is a slow walk, careful, the way a person walks on a roof they know is not theirs.
It stops at the tower foot. It does not come back. There is no sequence west to east, ever, and there is nowhere to go at the tower foot except down the tower, which is locked, or off the roof, which is a fall.
What the monitoring company does.
They stopped calling me in the second year, by agreement. The event is on their log as a known false activation at that site, nightly, and their contract has a clause for it, and my premium has a note on it.
The insurer's assessor came out once, and looked at the log, and looked at the camera, and asked whether anybody had ever been up there at one, and I said I had, with a torch, eleven times, and he said he would not have.
What is done about it.
The roof is alarmed and the alarm works, because in 2022 two men came for the lead at three in the morning and the sensors logged them and the police had them, and the log for that night shows their footsteps, and, an hour earlier, the walk.
What I do.
I read the log in the morning.
The one thing I have changed is that I do not do the roof inspection alone.
The architect's inspection is once a year, up the tower and out onto the lead, and I used to go up with him and stay on the roof while he measured, because it is a fine place to be on a summer morning.
In the summer I was on the lead at the east end while he was at the tower foot writing, and the sensors under my feet, which log by day as well as by night, logged me standing there, and then logged a sequence starting beside me, at the east end, and going west along the roof, sheet by sheet, at the slow pace, past the architect, who looked up, and to the tower foot, where it stopped, and the monitoring company rang my phone in my pocket to tell me somebody was on the roof, and I said I knew.