Amazon.com: 2Sets Magnetic Reed Switch Normally Open Closed NC NO Door Alarm Window Security/Magnetic Door Switch/Magnetic Contact Switch/Reed Switch for GPS,Alarm or Other Device,DC 5V 12V 24V Light : Electronics
BOSCH, Radion Series, Wireless reed switch, For doors/windows, Surface mount, Suits RFRC-STR2, RF3212E, B810
Door Opening GSM alarm Wireless home security system using Arduino
Autowatch 659000 Compact Wireless Reed Door Switch Sensor for Alarm - Base Systems
Bosch RFDW-SM-A Door Window Contact, Wireless Surface Mount
106-091 NESS RR3 MICRO RADIO REED SWITCH
Reed Switch - COM-08642 - SparkFun Electronics
Wireless Reed Switch for LA5290 or LA5145 | Jaycar Electronics
Magnetic contact switch (door sensor) : ID 375 : $3.95 : Adafruit Industries, Unique & fun DIY electronics and kits
Amazon.com: 5Sets Magnetic Reed Switch, Magnetic Door Switch/Magnetic Contact Switch/Normally Open Closed NC NO Door Alarm Window Security, for DC 5V 12V 24V Light (Black-B31) : Industrial & Scientific