Miniature Loop Alarm:  (circuit design added 8/03)

Minimizing SUN's Noise in IR Reception:  (electronic Circuit / Schematic added 10/04)

Modular Burglar Alarm:  (design circuit added 8/02)

Motorcycle Alarm:  (circuit design added 8/03)

N/O: N/C Timed Burglar Alarm :  This is a simple but effective alarm circuit which can reset its self after a time that you select. it has normally open and normally closed triggers which make this circuit very practical. This alarm has normally open and normally closed triggers. It's on a 555 timer so the alarm will reset it's self after a certain amount of time. The time is adjustable with the variable resistor in the circuit. The alarm has a reset switch which you can replace with a key switch to make it more secure, and you can change the triggers to other types of door or window switched too. The alarm uses a relay which is connected to a siren but you can replace the siren with whatever you want. The circuit is running off 9VOLTS but can range from 4V 16V.    (added 11/06)

Novel Buzzer:  (schematic added 11/06)

Novel Buzzer:  (circuit design added 8/03)

Oscillating output improves system security:  02/06/03 EDN Design Ideas  /  (added 1/05)  Many electronic-control systems have digital outputs that use transistors. One method of improving the security in these outputs is to use an oscillating signal to represent a logic-high state instead of a fixed voltage level (Figure 1). This type of signal, a dynamic variable, can drive the circuit shown in Figure 2....

Perimeter Monitor:  Using a single cable such as speaker wire or doorbell cable, this circuit can be remotely positioned, for example, at the bottom of a garden or garage, and used to detect all sound in that area. The cable can be buried in a hosepipe or duct and is concealed out of sight. The mic is an ordinary dynamic mic insert and should be housed in a waterproof enclosure with the rest of the circuit. (added 8/03)

Personal Alarm :  This one is particularly loud even though it runs on only two AA batteries. It uses a Push Pull transformer output   (added 2/05)

PIR Motion Detector:  (circuit design added 8/03)

Programmable Digital Code Lock:  (electronic circuit added 10/05)

Proximity Alarm #2:  (circuit / schematic added 2/03)

RFID Reader Handheld:  Intersil Application Block Diagram  (app note added 6/06)

Security CCTV:  Intersil Application Block Diagram  (app note added 6/06)

Simple Alarm System:  (circuit design added 8/03)

Single Button Lock Provides High Security:  03/04/99 EDN-Design Ideas / (added 5/03) Figure 1 is the block diagram of an easily programmed, single-button combination lock. You operate the lock by using a series of short and long pulses from a momentary switch that masquerades as a doorbell button. The circuit uses inexpensive CMOS logic. The retriggerable timer, T1, locks out entries made after the T1 code-entry window, thereby greatly enhancing security. The circuit in Figure 2 operates as follows: The Schmitt-trigger quad NAND gate, IC1, debounces the code-entry switch and, with the aid of simple analog circuitry, produces separate outputs for activation times of less than and more than 0.3 sec. These outputs connect to the select gate, IC5. The initial entry also sets timer T1 to enable the decoded decade counter, IC3. Each entry clocks IC3.

Single Zone Alarm:  (circuit design added 8/03)