Not included on the list is a burglar
alarm and remote monitoring. These things
lead to the inconvenience of arming and
disarming the system, expensive false
alarms, and monthly charges, and won’t
stop a burglar with quick fingers and a fast
getaway. For me, locked doors are my first
and primary line of defense.
Another hour stuck at the airport and I
had my design. A couple of weeks later, it
was installed and has been working reliably
for the last 25 years. In retirement, I now
have time to write about it and share it with
Some kind of sensor will be needed to
indicate the locked or unlocked status of
each door. I chose a mix of micro switches
and magnetic proximity switches. Each
switch is aligned to give a contact closure
when the door is locked. The details for
dead bolts, patio doors, and garage doors
will be explained shortly.
Next up is the indicator. A single
red/green bidirectional LED will do the job.
System status is encoded as follows:
• Red means the door is unlocked.