As it is 'keyless entry', it relies on the key transmitting its codes to the car. The battery in the key needs replacing.
We have had immobilisers in Europe sice 1998. There is a chip in the key, read by the car when the ignition is turned on. (Like the chip placed in a dog or cat). With keys inserted into an ignition lock, the chip is only energised by the electronic field around it, created by an aerial around the ignition lock barrel. With keyless, it needs to rely on the key transmitting its code, which it does all the time. For that reason, we are advised to place the key in a metal box, or 'faraday bag' once inside the house, as thieves can read the code from outside, and steal the car. Manufacturers have yet to add an on/off switch to the keys.
Most cars with this system will have a place inside the car which will read the key in the same way as normal key entry systems. This is usually somewhere on the centre console. The handbook will advise. Sometimes below a rubber mat will be a key symbol. Place the key there, it shoudl then recognise it.