Sensors for use at a small Motel

Other Hardware Sensors
1

Okay, most of my previous posts have been quite vague regarding my "projects", but this one will be far more specific.

I run a small motel and am in need of advice regarding different sensors for knowing when a guest arrives. Here is the Google Street View link of the front of the motel (images were from late summer 2009).

Currently I use a combination of a Door sensor that detects when the office door opens and closes AND an X10 wireless motion sensor that turns on a light in my house (which is the larger building with the carport and office). Before I had the X10 set-up, I would only know when a potential guest had arrived when the door opened and the chime went off, causing me to scramble to find where I had set the reservations book. Adding the X10 set up allowed me a minute or so to get my barrings and be ready when the guest walked into the office. Plus if I was in the middle of playing a game or watching TV, I would see the light go on rather than not hear the chime due to too much noise.

There are two doors into the front office, but only the one that is next to the car port is being used. The other we have blocked off. The door sensor is a RadioShack Wireless Door Chime, Cat. No. 63-874A, which Radio Shack apparently no longer carries, nor have I been able to find other similer units where the Chime and the sensor are seperate units (useful for me as I can carry the chime anywhere around the motel and my house).

The problem I started noticing with the motion sensor is that if a Semi drove by it would shake the building enough to trigger the light to turn on.

What I would like to do is have a more combined sensor set up, possibly with multiple sensors at the car port to act as a triangulation of sorts, and have a better chime for the door.

SparkFun has these sensors that look like they could work good for the replacement door chime. The current door chime sensor, I believe, is a Hall Effect Sensor, but I also notice that it sometimes goes off, sometimes doesnt, even with fresh batteries in both the sensor unit and the portable chime unit. This part from SparkFun looks like it is just an IR version of a laser trip wire.

As for the sensors at the car port, I am not sure what to use. The X10 unit is currently mounted facing straight down from the top of the CarPort, but it tends to also pick up cars that drive past the side of the car-port, not something that I am really in need of.

I still want to keep the "light turns on when sensor is triggered" feature, but I am also thinking of having a box mounted on the wall with a smokey white pane of plexiglass that has "Car Port" written on it, rather than turning on a lamp like I currently have it do, and maybe have a few of those spread around my home and the small fenced in back yard.

Any suggestions would be great, or even other ideas for sensor/automation that I may have missed.

EDIT: I also took one of the Radio Shack door sensors (one that didn't seem to work anymore, another reason we don't use that second office door), opened it up and looked at the circuit. The only IC on the board is a TC4069UBP, the rest appears to simply be resistors, capacitors, transistors, a button, an led, a 3-position switch for setting the frequency it is on).

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What would be wrong with the infrared tripwire things across the driveway? Do you get walk-ups? In that case between the posts of your porch?

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my only two worries about the IR trip wire would be the ambient light during the day and that those posts are not solid to the ground, they are simply facades that are connected up top, so vibrations will be worse when cars go by. In addition, we get snow and any trip wires that are low to the ground could potentially be disrupted. The car port sensors would need to be high up.

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I used a IR trip wire, similar to the ones used on garage doors, to sense cars coming and open a gate. It responded to ambient light when it got real bright outside, but a simple black pvc tube about 4 inches long fixed that (I painted a piece of 2 inch pvc with muffler paint). The sparkfun device looks like exactly what you need for the door. The rest of it is just code on an arduino and some wiring. Unless you want to go wireless.

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OP, I suggest a sonic ranger. Your car port ceiling probably is at least 7 ft high and a car parked in it will reduce the distance considerably. So hang a sonic ranger facing down from the ceiling and have arduino sense distance. If you get say 7 ft, stay put, if you get 5 ft or less (trial and error needed) for at least 1 second, turn on the light. IR sensor is not good for large distance and laser trip wire gets out of alignment too easy since semi trucks tend to shake your ground.

What I did with a sonic ranger was a car reverse obstacle sensor and I was able to back my car against a garage (not mine;)) safely and close enough.