Quick Summary:
- Slide the fob latch, pull out the hidden metal key.
- Pop the door handle cover, use the key to unlock.
- Hold the fob to the backup reader, then press Start.
- Replace the fob battery promptly, keep receipts for reimbursement.
A dead keyless fob battery is one of the most common surprises in a California car hire, especially after long flights, cold mornings, or if the fob has been pressed repeatedly in a bag. The good news is that most modern rental vehicles are designed with a mechanical backup to unlock the door and an electronic backup so the car can still recognise the fob and start. If you know where to look, you can usually avoid locksmith fees and unnecessary tow charges.
This guide walks you through practical steps: how to find the hidden key inside the fob, where the emergency keyhole is, how to start the car using the backup reader point, and what to do if the car still will not unlock or start. These steps apply across many makes found in California fleets, including Toyota, Honda, Nissan, Hyundai, Kia, Ford, Chevrolet, Volkswagen, BMW and Mercedes, though the exact locations vary.
Step 1: Confirm it is the fob battery, not the car battery
Before you start disassembling anything, do two quick checks. First, try the fob right next to the driver door and then next to the start button. If it only works at very close range, that strongly suggests a weak fob battery. Second, look for any signs the car itself has power. Do the interior lights come on when you pull the door handle, or does the instrument cluster light up when you open the door manually? If everything is completely dead, you could be dealing with a flat vehicle battery, not the fob.
If you have a second fob (some rentals include one in the paperwork wallet), try it. If the second fob works, the car is fine and you are simply dealing with a dead fob battery.
Step 2: Find the hidden mechanical key inside the fob
Nearly all keyless fobs contain a small metal key blade. It is there specifically for the dead battery scenario. Common designs include:
Slide-release fob: There is a small switch or button on the back or side. Hold it and pull the metal key out.
Push-button release: Press a small button near the key ring loop and pull the blade free.
Flip-out style: Some fobs have a key that flips out after pressing a release, though this is less common on newer push-start models.
If the key will not slide out easily, do not force it with a knife. Press the release fully and pull straight. If you are in an airport garage in California, better lighting helps, so use your phone torch and look for the tiny latch.
Step 3: Locate the hidden door keyhole and unlock the car
Many vehicles hide the keyhole to keep the design tidy. The lock is usually on the driver door, but it may be concealed under a small plastic cap near the handle. Typical locations are:
Under a handle cap: Look for a seam or a small notch on the underside of the driver handle. Some cars include a small slot where the metal key or a flat edge can gently pry off the cover.
At the rear of the handle: On some models, the cap is on the end of the handle closest to the back of the car.
Visible keyhole: Some vehicles still have an obvious key cylinder. Insert the key and turn to unlock.
If you need to remove a cap, do it carefully to avoid scratching paint. Use the metal key tip and pry at the notch, gently, then pull the cover away. Once the keyhole is exposed, insert the key and turn. If the key feels stiff, wiggle gently while turning. Do not apply excessive force, as some locks are rarely used and may be tight.
When you unlock with the mechanical key, the alarm may sound. That is normal. The car expects an electronic unlock signal, so it treats the mechanical unlock as a potential intrusion.
Step 4: Silence the alarm and start the car using the backup reader point
Even with a dead fob battery, the transponder chip inside the fob often still works when the fob is placed directly on the car’s backup reader. The car then recognises the fob without needing the fob’s battery-powered radio signal.
Use one of these common methods:
Push-button start vehicles: Hold the fob against the start button itself, or against a marked spot near the steering column, then press the brake and press Start. Some cars require you to press the start button with the fob, not your finger. Hold the fob so the logo or flat side touches the button.
Backup reader in the centre console: Some cars have a slot or a designated pocket in the centre console or cup holder area. Place the fob there, then press Start.
Backup reader in the glovebox or armrest: Less common, but some premium models have a reader in the armrest compartment.
Watch the instrument display for prompts such as “Key not detected” changing to “Key detected” or “Press brake to start”. If the car starts, drive normally, but replace the fob battery as soon as practical so you are not stranded again.
If you are travelling between airports and city locations, you might encounter different vehicle models on separate hires. Hola Car Rentals has guides for popular pickup points, such as San Francisco (SFO) car rental and San Jose (SJC) airport car rental, where keyless systems are common.
Step 5: Replace the fob battery safely and quickly
Most key fobs use a coin-cell battery, commonly CR2032, CR2025, or CR1632. The exact type is often printed on the old battery. You can usually buy replacements at pharmacies, supermarkets, hardware stores, and many airport shops in California.
To swap the battery:
Open the fob case: Many fobs have a small seam where the metal key was removed. Insert the key tip into the notch and twist gently to separate the halves.
Note the battery orientation: The plus side usually faces up, but confirm before removing.
Avoid touching the new battery faces: Skin oils can reduce contact quality. Hold the edge if possible.
Snap the case shut: Ensure the buttons click normally and the case is fully closed.
After replacement, test lock and unlock and confirm the car starts normally without the backup reader trick.
How to avoid locksmith or tow charges in California
A locksmith is often unnecessary for a dead fob battery, because the mechanical key should open the door and the backup reader should start the car. Charges rack up when drivers assume the car is immobilised and call for help before trying the built-in backup steps.
To reduce risk and cost:
Keep the hidden key accessible: If you share driving, show everyone how the key releases from the fob.
Carry a spare coin-cell battery: If you are on a longer California road trip, a spare CR2032 is small and cheap.
Do not leave the fob in the boot: If the car auto-locks, it can be hard to retrieve it without the mechanical key.
Confirm lock behaviour: Some vehicles lock automatically when you walk away, others do not. Test this once, in a safe setting.
If you need to change vehicles mid-route, it helps to know what’s common at your location. For example, airport and city fleets differ across California, including Avis car rental at San Jose (SJC) and Payless car rental in Sacramento (SMF).
What if the car still will not unlock?
If the mechanical key does not unlock the driver door, work through these possibilities:
You are using the wrong key blade: Some fobs store a valet key or a secondary blade. Confirm it is the metal key that came with that vehicle.
The keyhole is jammed: Try inserting the key fully, then gently wiggle while turning. Avoid snapping the key.
You found the wrong cover: On some cars, the lock is on the passenger side or hidden more thoroughly. Look for the small seam lines around the handle.
It is a different access system: A few models use a keypad or a phone-as-key system. In rental fleets, this is rarer, but still possible.
If none of this works, check your rental documents for roadside assistance instructions. At that point, contacting the assistance line is safer than forcing trim pieces.
What if the car unlocks but will not start?
If the door opens, but the car will not start even with the fob held to the start button, consider:
Vehicle battery issue: If the dashboard is dark or you hear rapid clicking, it may be the car battery. A jump start may be required.
Wrong fob: If you have multiple fobs (two rentals, or two drivers), ensure you have the matching one.
Brake pedal not fully pressed: Many push-start cars require a firm brake press. Some also require the car to be in Park.
Interference: Move away from large metal structures or other electronics. In airport garages, interference can reduce detection range.
Wet or damaged fob: If the fob got wet, the electronics may not respond even with a new battery. The backup reader still may work, but not always.
Model-specific hints you can try without tools
Because hire fleets vary widely in California, here are safe, general hints that often work:
Toyota, Lexus: Touch the start button with the fob’s logo side, then press. Hidden keyhole is often under a handle cap.
Honda, Acura: Hold the fob close to the start button, sometimes the back of the fob works best.
Nissan: Press the start button with the fob. Some have a reader in the console area.
Hyundai, Kia: Start button contact with the fob usually works, keyhole often behind a cap.
Ford: Some models have a backup pocket in the centre console. Push-start models typically recognise the fob near the steering column.
GM (Chevrolet, GMC): Reader locations vary, try the start button first, then console pocket.
BMW, Mercedes: Premium models may have a marked key symbol area on the steering column or console. Some use a slot style reader.
When in doubt, look for a small key icon stamped near a button, slot, or pocket. That icon often marks the backup reader point.
Good habits for the rest of your California car hire
Once you are moving again, take two minutes to prevent a repeat:
Photograph the emergency steps: Take a quick photo of where the keyhole cover is and where you started the car with the backup reader. It saves time later.
Keep the fob separate from loose coins: Coins can press buttons and drain batteries.
Avoid extreme heat: Leaving the fob on a hot dashboard in California sun can shorten battery life.
Know your pickup location support options: If you swap vehicles at different hubs, it helps to know the local desk procedures. Information pages like Enterprise car rental in Santa Ana (SNA) can be useful for understanding typical airport processes.
FAQ
Q: Will unlocking with the hidden key damage the alarm system?
It should not. The alarm sounding is a normal response to mechanical entry. Starting the car using the backup reader, or restoring fob power, typically silences it.
Q: Where exactly is the backup reader point on most push-start cars?
Most commonly it is the start button itself, recognised when you press it with the fob. The next most common locations are a console pocket, cup holder area, or a marked spot near the steering column.
Q: What battery do most key fobs take?
Many use CR2032, but CR2025 and CR1632 are also common. Check the old battery marking before buying a replacement, and match it exactly.
Q: The car unlocked, but still says “Key not detected”. What now?
Hold the fob directly against the start button and press the brake firmly in Park. If the dashboard remains dim or clicks, the vehicle battery may be flat and roadside help may be needed.
Q: Can I get reimbursed for a fob battery during a car hire in California?
Policies vary by supplier and rate. Keep the receipt and note the time and location of purchase, then check the rental terms or contact the provider for guidance.
