Ingress Protection describes the resistance to dust or water creeping into a device (such as an AED or Smartphone). The IP number provides a rating for the protection.
The IP number (or Ingress Protection number) comprises of 2 digits. The first digit is a rating for protection against dust particles. The second number is a rating for protection against water droplets. The following chart provides the type of protection indicated by the IP number.
| Key for IPX | Dust Resistance | Water Resistance |
| IP1X / IPX1 | resist dust particles >50mm | Dripping water |
| IP2X / IPX2 | resist dust particles >12.5mm | Dripping water when tilted 15 degrees |
| IP3X / IPX3 | resist dust particles >2.5mm | Spraying water |
| IP4X / IPX4 | resist dust particles >1mm | Splashing water |
| IP5X /IPX5 | Ingress of dust not completely prevented | Water jets |
| IP6X / IPX6 | No ingress of dust | Powerful water jets |
The highest IP rating for AEDs (as off January 2018) is IP55.
If there is an "X" where a number should be, the device was probably not tested for that resistance. Example: IPX3 means that the device was not tested for dust resistance, but has a water resistance rating of 3 (resistant to spraying water).