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
you.
The Design
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.
