Dear grererwhut,
You have two parts to your inquiry. Using a PIR sensor to respond when you wish and (2) receiving that response on your phone. Since the Oak is an arduino like device, it may be simpler for you as a newbie to work the first issue -- wiring and code for a PIR application-- out on an Arduino Uno using a PIR and code you can than migrate to the OAK.
Once you can detect your desired event locally, the Oak can send you your event notification over the Internet. This can be done using the Blynk application on android or iPhone. It can also be done using a browser or http: type notification using the Particle interface.
By the time you have the PIR and code working on a UNO using a simpler USB connection to your local computer, the second part should be more complete documented or have more examples here for you to follow. You will need a data plan on your phone or be limited to receving messages when you have a wifi connection. These routes do not use anything like a sms message, only internet access works.
Adafruit sells an appropriate sensor and they provide a wealth of links to arduino based use and application examples. If you start on their web page for the sensor, you will see links that lead to details of the PIR wiring and use and further links to application examples.
https://www.adafruit.com/products/189 There sensor is 3.3 V so no need for level shifting on moving to Oak.
They have an example on sending an email using an Uno and separate programing on you host computer to do the email. This python programing for sending an email can be replaced by using Blynk and/or Particle communication from the Oak. This example:
https://learn.adafruit.com/arduino-lesson-17-email-sending-movement-detector/arduino-code has as its first step a simple sketch that uses your computer monitor and serial communication. All you have to do is change the Serial.println() output to Particle.publish() output to get a web enabled notification working. You can build from there.
Getting the output as you want it on your phone once you are getting Particle log communications from you Oak is something you can tailor to your phone and needs. It is also something you can ask for more specific help with once you are at that point.
Cheers.
James
PS Looking further down this forum list, there is a note on using Oak or similar devices to send SMS by a couple methods, depending on the carrier you have etc. you may want to look at this since SMS notification would remove the requirement for internet access. See
https://digistump.com/board/index.php/topic,1786.0.html lower on this page